Is your feature request related to a problem? Please describe.
Currently Mycroft attempts to download the Precise engine and model if it cannot find the compressed tarballs. The extracted contents may be present and working, but it will download them again.

Describe the solution you'd like
We should update this process to detect whether the contents exist and are callable.
We may want to add a mechanism to download a fresh copy in the event of failure / corruption.

This will mean we can preload the extracted Precise and not need to leave the compressed tarballs on disk.