notify: re-factor email code

specify default emails on initialize
updated notify to accept arguments
notify: added email notification and state information queries
notify: use constant enum instead of strings for state
notify: removed env references and hardcoded respective values. Using enum for state
notify: added failover interval code and moved notify to base
Merge remote-tracking branch 'origin/notify' into notify

Conflicts:
	lib/nerve/leader_watcher/base.rb
	lib/nerve/service_watcher.rb