[#620] Added keyword models and admin entries
[#260] Added keyword filter logic to partner sites and widgets
[#260] Cleanup code on several places
[#620] Removed ProjectKeyword and PartnerSiteKeyword models
[#620] DRY up project selection code
[#620] Added keyword column and filters to admin
[#620] Moved show_keywords to utils and added keywords to TastyPie API
Merge pull request #645 from akvo/feature/620_partnersites_keywords

[#620] Added keyword filtering for partner sites