added quota limit support
worked in comments to c4ae663 by @ogasser
worked in comments to ab1a1cd by @ogasser
fixed size calculation
More changes before testing and merging quota branch

* JS: Added extra checks for empty string
* Changed some language strings
* Changed spaces to tabs, space fixes
* Added more documentation
Merge branch 'robomod_quotas' into mozilla_sync_1.2

@RoboMod implemented quota for Mozilla Sync. This allows the ownCloud
administrator to set a global space quota. Sync clients are only allowed
to sync less data than the curent quota.

Closes issue #32.
Closes issue #39.

Conflicts:
	lib/storageservice.php
	lib/user.php