Move cache location methods so they are available in all builds

Add support for specifying fixed RTK base position

Stable desktop version check

Remove unused code

Also hand carried text to speech changes from Stable to master. Plus
unit tests for that.

Switch test from 8.8.8.8:53 to "www.github.com:80"

Signed-off-by: Patrick José Pereira <patrickelectric@gmail.com>

No more user prompting

Convert bool settings to SettingsFact

Made QGCCorePlugin derive from QGCToolBox and expose everything through the same mechanism as everything else.

- Convert mission load/save to it
- Allow parameter load/save on mobile

Also additional major Mission usability changes