Implement SwipeRefreshLayout

Forced sync is now possible by swiping down like e. g. in the G+ or
GMail-App.
Only enable swipe refresh for own list
Don't try to sync if there is no connection
Use synctask() for forced sync

forcesync() has done the same, so it was implemented twice (thx @ratan12
for pointing at it).
Fix notifications for synctask()

Only disable notification for swipe refresh.
Don't use holo colors from android resources

They are available for API 14+ only
Show loading indicator if forced update and clear=true
Merge pull request #180 from d-sko/swipe_refresh

Implement SwipeRefreshLayout
Switch to Account manager, syncadapter & contentprovider.

Changes in short:
- Cleanup unused imports
- Rewritten auto-sync (Works now on the background)
- Prefs user/password has been moved to the safe account manager
- Updated androidmanifest for the requied permissions
- Added/Removed strings
- Removed old settings
- Updated login screen (use accountmanager)