Expose `event` in config

This allows safer generation of events from riemann streams.
Catch events missing time when indexing

Currently, events missing time throw a NullPointerException.
Initial attempt at slack notifications
Load slack support and tests
update tests to new indexing behavior
Mark slack tests as integration
refactor slack notifications and make them work
Merge pull request #353 from pyr/feature-catch-no-time

Expose `event` in config and catch events missing time
Drop warning from core index wrapper for events without time
Merge pull request #354 from gsandie/add_slack_notifications

Add slack notifications
Deprecate combine in favor of smap
Fix exception message regexp
use correct form
Merge pull request #358 from pyr/fix-two-bugs

Fix two bugs