feat: add class stats to professions

feat: add class stats to professions

When you select a profession, there are a certain number of stats that
are considered "class stats". They may automatically increases on level
up.

For example:

Warrior class stats: Strength, Constitution.
On even level up, you gain +2 strength, +1 constitution
On odd level up, you gain +1 strength, +2 constitution

Class stats only cost a single stat point to increase, and non-class
stats cost 2 stat points.

You only ever gain 1 stat point on level up.

Wanderers are a special profession that do not gain any stats on level
up.. but all stats are considered "class stats"