Refactored the Aodh notifier class

 - Included alarm actions to send notification to SO
 - Utilizes Aodh's webhook option for alarm_actions
 - Included additional tests for this change
 - Updated documentation

Change-Id: Ia3f2e2fa2ffee0cc66a80d5098d52b7da2be2dbe
Signed-off-by: Helena McGough <helena.mcgough@intel.com>