Bug-fix release.

Receive
- Fixed a duplicate session record when closing the results screen
- Fixed "Next" right after the 20th character starting a 21st question
- Sessions you quit early are no longer recorded
- Added a Delete button for group input; Replay no longer clears what you typed

Send
- Callsign drills now use only the characters you have learned
- Keying that does not form a valid character now counts toward your stats

Other
- Purchase pending/failed and restore results are now shown. You can retry loading the price when it is unavailable
- Fixed the vibration setting not being applied on launch
- Audio engine stability improvements