include category network

[foobar0112]

• content: include more categories from various othe rprojects
• improvement: check/ add connections
• backend-dev: provide special API for categorie
• frontend-dev: provide categories to navigate trough project database (in a nice way)

[foobar0112]

..and split this issue up ;)

[fmhc]

maybe it would be interesting to have that in multiple languages? hrhr :D