make skill and category system

- [x] skill model
- [x] skill model fields: mate, name, category, rate:float
- [x] rate under paper trail
- [x] skills/categories should be assigned for specific date (calendar here)
- [x] ability to remove skills
- [x] teamate skill is allowed to be created only by team owner
- [x] teamate skill is allowed to be edited only by team owner
- [x] teamate skill may be removed either by team owner or by teamate himself
- [x] appropriate visibility for links
- [x] graphic representation of skill level history on skill page
- [x] graphic representation of skill levels on skills page of mate
- [x] crunch data by category for each user upon skill saving
- [x] graphic representation of category levels on profile page
- [x] skills should be searchable from existing, sorted by frequency
- [x] categories should be searchable from existing, sorted by frequency
- [x] setting skill level graphically
- [x] highest skills/categories reflected at user profile page
- [x] list of teams user in on profile page