New version of category/categories input type

The current version of categories input type numerous issues.
Most critical is that you can not select any subcategories
after opening new nodes in the tree view.

This commit replaces the current input types, based on CategoryTree
with a new javascript tree-view, utilizing the dynatree library
(https://code.google.com/p/dynatree/) It is designed to be feature-
compatible with the old input type, except that it doesn't include
the "use dropdown" option of category input.

A working example can be found here:
http://ec2-46-137-28-172.eu-west-1.compute.amazonaws.com/wiki/index.php?title=CategoryTestPage&action=formedit

Updated to give correct behavior when page contains both category and categories input, and use radio buttons for category input

Revert accidental update of loading.gif
Change-Id: I546caff26b87b9a640a778d8a129d8132c21f940
Merge "New version of category/categories input type"