Allow for multiple sets of keystores

In regards to SSL/TSL certificate management, Openfire by defaults supports one set of key stores (one that acts as an identity store, and two that act as trust stores, for s2s and c2s connections respectively.

Having one set is not enough for some users. Some would like to use different stores for BOSH, for example. Also, splitting off the webadmin certificates from the XMPP functionality can make sense.

Openfire should allow more than one 'set' of stores.