Don't hardcode strings!

This avoids translations.
Clean up & add missing strings

But please, check if these values ​​can be deleted, if they are really useless.
Added a explanation.

"headset_connect_player_summary" = Launch the default music app when headset is connected
More hidden features

If Pie is disabled, you can do nothing.
Fix
Merge pull request #41 from AirOne70/jb2

Let's be more user friendly.