Probably happened due to copy/paste mistake or something

[kaos branding] Fix broken link

Create a new module and branding targeted at the smartphone and tablet
use case. The installation process is significantly different from your
typical PC install:
* The UI must fit mobile screens, the amount of inputs visible on one
  screen must be reduced.
* Every input must be controllable with an on screen keyboard.
* Full disk encryption is done with GRUB in Calamares, but mobile
  devices use other bootloaders (u-boot, lk).
* Complex partitioning screens are not useful for most users, as the
  expectation is not that multiple OS can be installed next to each
  other.

It would be nice if the regular Calamares modules worked with mobile
devices eventually. But this can't be done in one step (and before that,
the QML <> QWidgets related refactoring should probably be completed?),
therefore let's add it to calamares-extensions first.

This initial version is far from perfect, but what is there works
reliably. It should give a good shared base to iterate upon.

Implemented screens:
* Welcome
* Lockscreen PIN
  Set the user password, but as numeric PIN. Because that is what the
  current generation of mobile friendly Linux DEs expects (Plasma Mobile
  and Phosh).
* SSH server: enable or disable
  To debug Linux distributions on phones, SSH is essential. Give
  advanced users the opportunity to enable it and casual users the
  option to skip this.
* Credentials for SSH server
  The SSH server has a dedicated user account with a stronger password.
  Users are encouraged to replace password auth with SSH key auth after
  the installation.
* Full disk encryption: enable or disable
* Full disk encryption password

Screenshots:
https://postmarketos.org/blog/2020/07/15/pinephone-ce-preorder/#installer-with-optional-ssh-server-and-encryption

There is no partitioning screen. The target partition, which will be
formatted and optionally encrypted is defined in mobile.conf as
targetDeviceRoot. It is expected that the installer OS will use this to
install to an empty partition on the same medium as the installer (SD
card or eMMC) as explained here:
https://wiki.postmarketos.org/wiki/On-device_installer

I ended up throwing everything into one module instead of several,
because of a Qt Virtual Keyboard bug:
https://gitlab.com/postmarketOS/postmarketos-ondev/-/issues/18

Based on, but adjusted to be distro-agnostic:
https://gitlab.com/postmarketOS/postmarketos-ondev/-/releases/0.2.1

[mobile] add mobile friendly module and branding

Find yamlcpp, even if it is named libyaml-cpp.so (with a dash) as it is
the case in Alpine Linux.

[mobile] use SPDX-FileCopyrightText

CMakeLists: add find_package YAMLCPP

Depending on compiler version and Qt version, this may or may not
compile; typical errors look like this:

/usr/include/qt5/QtCore/qlist.h:471:35: error: use of deleted function 'QPair<const QStringList, const QString>& QPair<const QStringList, const QString>::operator=(const QPair<const QStringList, const QString>&)'
  471 |     else *reinterpret_cast<T*>(n) = t;
      |          ~~~~~~~~~~~~~~~~~~~~~~~~~^~~
/usr/include/qt5/QtCore/qpair.h:49:8: note: 'QPair<const QStringList, const QString>& QPair<const QStringList, const QString>::operator=(const QPair<const QStringList, const QString>&)' is implicitly deleted because the default definition would be ill-formed:
   49 | struct QPair
      |        ^~~~~

There's no need to name calamaresui -- viewmodules get that
automatically -- and if it *did* need to be named, it would
be Calamares::calamaresui

Organize the screens into features and replace all navTo() calls with
hardcoded screen names with new navNext() and navNextFeature()
functions.

Skip whole features if a featureSshd (example for feature "sshd") or
smilar config key exists and is set to false.

Add featureSshd config key to hide related UI screens and skip related
logic in UsersJob.

[mobile] make sshd feature optional and related navigation refactoring

Fix a typo and make the "booleans we don't read from QML don't need
a signal" message generic with one example, but not with a listing of
all these booleans. Then we won't need to adjust this comment with each
new one.

Rename "enableButton" to "firstButton" and "welcomeText" to "mainText".

Don't create the user's job in MobileQmlViewStep::onLeave() anymore.
Instead, have Config::createJobs() and call that from
MobileQmlViewStep::jobs(), as suggested by Adriaan, and that's also how
it's done in the keyboard module in calamares.git. This allows getting
rid of m_jobs, and makes it less awkward to pass parameters to the job.

Related: calamares/calamares-extensions#6 (comment)

….4.0

- remove inline comments from upstream, link to upstream files instead
- remove settings that match upstream defaults
- reformat

There's really no chance of 1GB of RAM being able to eval a NixOS config.