This patch makes class registration an opt-in function, in most cases 1 line in the existing register() function is enough.

- removes registration as an automatic action.
- adds a convenience function to register classes from a module (rather then registering all classes in a list as was done before).
- fixes bug [#24132]

Note:
- Applies to svn r34490
- Only updated addons: netrender and Renderfarm.fi, all other addons will be updated too if committed.