Merge some more changes from team/russell/events

This commit pulls in a batch of improvements and additions to the event API.
Changes include:
 - the ability to dynamically build a subscription.  This is useful if you're
    building a subscription based on something you receive from the network,
    or from options in a configuration file.
 - Add tables of event types and IE types and the corresponding string
    representation for implementing text based protocols that use these
	events, for showing events on the CLI, reading configuration that
	references event information, among other things.
 - Add a table that maps IE types and the corresponding payload type.
 - an API call to get the total size of an event
 - an API call to get all events from the cache that match a subscription
 - a new IE payload type, raw, which I used for transporting the Entity ID in
    my code for handling distributed device state.
 - Code improvements to reduce code duplication
 - Include the Entity ID of the server that originated the event in every event
 - an additional event type, DEVICE_STATE_CHANGE, to help facilitate distributed
    device state.  DEVICE_STATE is a state change on one server, DEVICE_STATE_CHANGE
	is the aggregate device state change across all servers.


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@121555 65c4cc65-6c06-0410-ace0-fbb531ad65f3