Add parsing support for charges and Volatility

[maybenomad]

Description of the problem being solved:

• Adds parsing support for power, frenzy, and endurance charges
• Adds parsing support for "gain Volatility on kill" mods

Steps taken to verify a working solution:

• Checked PoB UI for support
• Manually evaluated ModCache.lua to ensure proper results

Other discussion:

The "% chance to gain " modForm that resolved to "FLAG" was swallowing all charge and volatility mods. I resolved this by deleting this line entirely (it was only used for the "Arcane Surge on Crit" mod) and modifying the "CHANCE" parsing step to allow modType overrides.

I would like some feedback on this approach. My other idea for addressing this was to keep the "% chance to gain" modForm line but resolve it to a new form called PROC. When parsed, PROC mods would first check for a matching flag and then move on to scanning the modNameList if one is not found.