Minor refactoring

* update target SDK version to API level 19
* less null return values
* explicit Resource generateUID/generateName methods
* use StringUtils when it makes sense
Allow vCard4 fields (ANNIVERSARY) in vCard3, too (closes #131).
Use (final) static wherever possible for method signature clarity/performance
Bug fixes

* optimise URL repairs: don't replace "[", "]", ":" in host names, allowing IP address literals (closes #98)
* SyncManager: minor refactoring
Commit after every full record insertion/update (closes #135)

Docs say that TransactionTooLargeException is thrown when the buffer reaches 1 MB. Because we can't know
how large a single insertion/update is and there may be contacts with larger photos, it's only safe to
commit after every insertion/update. If photos exceed ~ 900 kB it would be required to write the photos
to an asset file (maybe I'll do this later, then we can group insertions/updates again).
Version bump to 0.5.5-alpha
0.5.6α Wage Slave

* support primary (preferred) phone numbers/email addresses
* fix (crash) bug in URI sanitation
* don't set calendar properties not supported by device's Android version
* require already-set remote file name when finding updated records
* version bump to 0.5.6α
Merge remote-tracking branch 'blessed/master'