Attributes and Skills ruleset update v7

[CodeWringer]

• [x] Enable manually keeping track of modified and unmodified attribute and skill levels.
• [x] Skills are now divided into three tiers, based on their level. The requirements to advance are different by tier.
  • Level 0: 6 S / 9 F
  • Level 1-4: (N + 1) 2 S / (N + 1) 3 F
  • Level 5+: N N S / (N + 1) (N + 1) F
  • Where N = current level

[CodeWringer]

Modifier-logic moved to #212