added jquery ui icons. otherwise its for casual users impossible to close the new event dialog in the calendar

Filled username field when oc_username is set repaired.
Problems with "advanced settings" button in installation wizard fixed.
CSS improved - login and installation now looks more clean.
Request password link removed (email feature not implemented yet).
Database radio button bugs removed.
It is possible to have an empty database password, now ownCloud will support this "security issue".
Ignore Mac OS X ".DSstore" files.
Fade in/out of login button and remember checkbox removed due to some display errors.

Create OC_JSON class, for single point of creating json responses.
No real logic change, this just cleans up the code a bit.