Added logic for derivation of the score field in the CharacterSkill model
simplified logic on skill calculation in the CharacterSkill model in models.py

Also, forgot to mention on last commit, updated models.py
added proper defaults for fields and finished filling out lookup fields
added a number of derived fields to the models in models.py
also ran validate and cleaned up some errors in existing code
Merge branch 'models' of https://github.com/Ichimonji10/gurps-manager into models

Conflicts:
	apps/gurps_manager/models.py
fixed conflicts
In models.py
Added total_points_in_advantages and total_points_in_disadvantages fields to character model
In models.py
added total_points_in_special_traits field to character model
fixed a couple derived fields to have the self parameter
In models.py, added several derived fields on the character model
all models should be ready for testing