Added actions to manage modules (manually adding/removing symlinks for now).
simple form for enabling/disabling owncloud module
Make module manager work for any available modules.
Combined module management actions into a single file, so it should be easier to add new optional modules.
Instead of a separate page and form classes for ownCloud module, just need one class that does both.
Merge pull request #59 from jvalleroy/module-manager

Merge: James Valleroy's Plinth Module Manager