Updated capability manager

Referenced charybdis commits:
 - e679e389067be7318cf0f99858b5ff84fac9104b (capability: do not use strings provided by modules for keyword index, instead duplicate the keyword: mogri)
 - e915e51f4d53b75bd2dad31ef64adc2118ae7c58 (capability: don't use DictionaryIter internals: mogri)
 - 8bedf01d19e4aff208d355a3b43751ea40f798e0 (capability: store capability bit entries with actual bit numbers, instead of an actual mask: mogri)
 - bde42c60639cf25429614a94771c739e661b667b (Don't shadow the name "index": jillest)
 - 885cd603b516c533dcf6788d684a5189fe1b15ef (capability: add global list of capability indexes, and name all capability indexes: mogri)
 - a16910aa4e95a18eff20842cd3516f8dd33dba8e (capability: add capability_index_stats() for getting statistics about the capability broker system: mogri)
Missed a variable