Map-specific perk config

[Phil25]

There are two configs considered for perk configuration: rtd2_perks.default.cfg and rtd2_perks.custom.cfg. Since perks cannot be configured per map (only disabled), this mechanism could be extended to allow just that.

Example:

• Presence of rtd2_perks.ctf_2fort.cfg will alter perks when 2Fort is the current map.
• rtd2_perks.pl_%.cfg will alter perks for every map starting with pl_.

Order of overrides:

1. default
2. custom
3. map-wildcard
4. map-specific