Implement Skills and Proficiency System

[Ijwu]

Create a skill system that tracks proficiencies. It should be expandable and easy to add new skills to.

Requirements:

• Database (Implement a database of some sort. #4) to keep track of each player's skills.

Reasons:
We should have the ability to track skills and their levels. This is important in order to have player classes and player crafting.

Notes:
Preferably, the system should include these things:

• It should be easy to expand.
• It should allow for skill prerequisites.
• It should allow for skill progression.

[Ijwu]

I've just been informed that classes are for suckers and "Sword Art Online didn't do classes."

We could also just do a free-form "learn what you want" system.

[Olink]

Most of this is implemented in 901255a

Left to do

• Implement static access to the global skill list in skill_store
• Fix logic in skill_set.check_unlocks to reference above
• Fix logic in skill_wrapper.add_exp to get the exp table from the above
• Save in player database

[Olink]

I think, before I dropped this project, that all of the above were done (minus the database parts). Will close this and add an issue for database backup/saving.