CFD-202 : Split og vocab facet

Spliced the facet in 2 new facet blocks:
- Group Categories
- Group Tags

Added extra facetapi sorter so we can sort terms by their weight.

Added extra facetapi widget so we can group taxonomy terms by their level 0 terms (used for Group categories).

Added missing geo tags to discussions.

![c4m-discussions-overview](https://cloud.githubusercontent.com/assets/133124/5179890/1a53c16e-7485-11e4-9624-8fb57cb4ecba.png)



The c4m_og_vocab module is created in that way that one group type can have other automatically created og_vocab vocabularies then another.

E.g.
You could have:
* Group : Categories & Tags.
* Project : Only categories.

Could be that we never need the difference but since the c4m_og_vocab modules upports it, so should the alter callback.