IRCd:abstracted database

IRCd-darenet currently keeps a database of all users, servers, and channels on the network. All data that must be kept about one of these entities must be explicitly declared in the structure describing that entity. The proposal here is to simplify the database, keeping only essential information, and making some of the more advanced information available via an "ancillary data" interface (already commited to the trunk). Furthermore, a unification of the concept of an "entity" is in order; currently, you have channels and clients, the latter of which may be subdivided into users and servers; this proposal creates an entity, which is subdivided into channels, servers, and users, and possibly services.