[unit configs] Remotely disabling units

Imported From: http://groups.google.com/group/in-portal-dev/browse_thread/thread/f7c373b195d119c9#

Right now unit configs are automatically discovered in all installed modules.

To prevent In-Portal from discovering units we currently must add "." before unit folder name. However it's not possible with third-party modules, like "in-link".

Solution

To solve this problem I'm proposing to create a database table called "SystemUnits", where all units will be added, once they are firstly discovered. Then we can create a new section, where units will be managed.

This way if we completely need to get rid of a specific unit in a module, then instead of reverting changes made from it we just disable it in first place and no changes will be made.