fix: Cleanup and renaming

Renamed attributes (mostly variables.)
intellect > intelligence.
social > socialStanding.
psionics > psionicStrength.
Removed unused compendiums/packs, will re-add as needed.
Added empty compendiums for skill lists that will be added first, ce-skills.db and 2e-skills.db
Add 'key' to all skills and characteristics, which is the key to reach it in the skills object. (Mainly to make things a bit easier in the code later. Basically a human-readable id, must be unique and match the actual key, though nothing really enforces it yet.)
Rename skill.characteristic to skill.defaultCharacteristic.
Add skillType to skills. (Intended to be either 'basic' or 'weapon', with weapons eventually having special handling. Maybe other types would be useful?)
Added notes about bugs and changelog to system.json
Made sure currently used skill names match OGL (UMP 'Skills_list_2e.doc') and not some other variant. (In preparation for adding more skill lists.)
Added skillSource to all skills (currently all are set to 2e to match the above.)