added select all actionbar item on main (inc archived) and compose activities. item becomes available when first item selected. menu item toggles select all/select none.

added indefinite timeout to archive snackbar on conversations activity when >= 10 conversations are archived at once. in case of accidental mass archive gives user more time to undo.

added 'show status' menu item on compose activity that does the same as short touching on an item (expands it to show time, etc) but can be applied to multiple selected items at once.

made some actionbar items on conversation/archive and compose screens always displayable to maintain user experience whether one or more items are selected on those screens.

select all allows faster actions for 'mark all (un)read', archive all, delete all, pin all, block all, copy messages text (in compose), delete mesages (in compose)

new select all actionbar item available on conversations and compose screens when at least 1 item selected;

new show status item on compose menu when at least 1 item selected;

largely satisfies #141 by enabling; select all -> mark read; for quick mark all read

satisfies item 3 in #53 - 3. Select all conversations...

largely satisfies #134 - display time for all messages by enabling select all -> show status