[Owncloud] merge request #134: Fix for oc-972, oc-1144 and oc-1191

[Johannes Willnecker]

Hello all,

I just created this merge request please review it and let me know when
there are problems with this merge request.

The problem described in the three bug-reports was introduced with the
commit
https://gitorious.org/owncloud/owncloud/commit/76f20eb57c4089b51ee506a000a21ab95727da43

When the thumbnail size was not stored in the database the gallery page
itself tried to resize the images.
With this fix only the thumbnail size will be calculated within the
gallery page but the thumbnail itself will be
created by the apps/gallery/ajax/thumbnail.php script.

Regards
Johannes Willnecker