New index system, idx()

Transitioning to idx() as the index to the various data matrices.

Remove current_max_bonuses, current_pve_max_stats, current_pvp_max_stats.
current_pv._maxes now contain both bonuses and stats.
This creates a redundancy in the bonuses, which will be addressed in a future patch.

Join max_bonus_ui and max_stats_ui into a single list; ui_names.

Update all code to use idx() indexing.

Factor out damage calculations, thereby adding all combinations of PVE/PVP and
dual/single wield.