Adding basic monitoring of drains & channels

Looks for orphans (both in ETS vs. drain, or channels vs. drains, in any
storage available).

Also looks at total drain and channel count, and compares it with other
nodes.
Fixing channel deletion to include drains

Channel deletion would delete only the ETS table entries for each drain,
leaving the door open for new nodes and NSYNC'ing to bring back dead
drains (that were not killed on existing nodes).

This patch makes it so that deleting a channel, which calls
logplex_drain:delete_by_channel/1 actually removes said drain via redis.
nsync callbacks will then clean up the rest.

Conflicts:
	src/logplex_drain.erl
	src/logplex_mon_serv.erl