Restructure profile models

[marcinjosinski]

• Moved common fields into BaseInfo and BaseMatchmakingInfo abstract models
• I decided to delete the company app and store these models in the profile app because actually they describe profiles.
• Due to SRP, I decided to split validation into two phases:
  1. schema validation -> serializers are responsible for this phase
  2. logic validation -> services are responsible for this phase

Also, I want to care about data integrity so:

• whenever I can use Django's constraints I do that.
• I use clean methods to be sure that I put clean data into my database.

This method has drawbacks too:

• introduces semantic coupling
• I have to remember to call full_clean before save()