OC_Util::setupFS($user) will create a data dir for the given string - no matter if the user really exists - OCP\JSON::checkUserExists($owner); introduces a ready to use check which will bail out with an JSON error

isPreviewAvailable wasn't always set as the files formatting code is
slightly different than the one from the files app.

Fixes #6423

necessary for https://github.com/owncloud/apps/pull/1476

Fixes #5534

Added missing condition to check whenever allowed zip size is unlimited.

Fixes #3717

 * Works in IE8, 9, 10, Firefox 24 and Chromium 30
 * Credits to Julian Müller @Julian1998

when _ is left in namespace and files are named after their classes the autoloader will also find classes in the lib folder of an app
its magic!

Frontend:
- The files app list now uses ajax calls to refresh the list.
- Added support the browser back button (history API).
- Added mask + spinner while loading file list

Backend:
- Added utility function in core JS for parsing query strings.
- Moved file list + breadcrumb template data code to helper
  functions
- Fixed some file paths in trashbin app to be similar to the files app

No upload on pubic page if public upload is disabled

on reshares we now recursively move to the root of all reshares - therefore some code has been refactured and added as a new public function

for the public share was wrong.

Fix #2725