fix memory allocation bugs in whisper.cpp

See merge request alex/voiceinput!3

Use whisper.cpp

See merge request alex/voiceinput!2

Manual migration screen - similar to download activity
Automatic migration - runs via JobScheduler and updates models automatically, if connected to network

To make it clear when you're using the dev build

Don't run encoder twice when detecting language. Limit decoding threads to 2

* Added theme selection
* Settings menu has a better look
* Move around some of the code