Prepare for syncthing v0.9.0.

This includes chaning the path from github.com/calmh/syncthing to
github.com/syncthing/syncthing, as well as disabling updates from
the web gui
(https://discourse.syncthing.net/t/v0-9-0-upgrade-from-within-gui/537).
Bumped version to 0.4.4.
Fix crash if no QR scanner is available (fixes #71).
Log error code on syncthing binary crash for better logcat searchability.
Add options to stop sync when not charging or not on wifi (fixes #15).
Start automatically on boot (closes #54).
Extracted SyncthingRunnable into seperate file.
Removed exit button (closes #6).

This has become useless, as the service would be automatically restarted
whenever a network/battery/boot intent is received.
Refactoring of config related functions/constants (moved ConfigXml).
Use Java 1.7.
Remove catch-all statement.