Schedule generation for Leagues should be a PORO and also be tested that way

[Askir]

Since Schedule generation is quite independent of the model itself it is way too much logic in the models class and should be extracted into a PlainOldRubyObject(PORO), that handles all the edge cases and encapsulates how the schedule specifically is generated.
Tests for this should also be extracted from league_spec.rb and could potentially use moc-objects for the event objects, to speed things up a little bit if needed.

What this accomplishes:

• Encapsulates algorithms into their own file and classes so that you don't have to search the huge model file for the correct lines if you want to change anything
• Decouples the algorithms from the League class so that in theory you can use them with other events aswell
• Improves readability, by allowing more names and more submethods without cluttering the model