safeslinger release 1.6.12

- Separated source for developers into easy exchange library and demo
for any Android application to use (github.com/SafeSlingerProject).
- Improved exchange UI to display better icons and selected values.
- Added setting to customize message notification: sounds, vibration.
- Added setting to change message font size (default is slightly
larger).
- Added setting to auto-decrypt messages (default to true).
- Fixed loss of selected attachment on Compose tab.
- Restored Sling Keys Assistant on Sling Keys tab.
- Replaced ActionBarSherlock library with appcompat-v7 library.
- Stability fixes.

NOTE: This commit replaces an earlier one yesterday with notes removed
that included user comments emailed to us. Since we did not have
permission to publish those comments, we’ve since removed those 2 files
of notes to respect our users privacy.