Added email groups and changed notif-profiles to selectively send to groups.

[abundy7]

We had the desire to send some alerts (such as disk 80% full) only to admins, and send other alerts (such as API is down) to admins and customers. This has be achieved by changing the email Receivers in the Key/Value store from a JSON Array to a Folder with nested Keys that represent email groups, and values that are Lists of receivers for the given group. For example:
...
receivers/
admins --> ["admin1@example.com", "admin2@example.com"],
customers --> ["customer1@somecompany.com", "customer2@anothercompany.com"]
...

The code was updated to handle this different Key/Value setup, with the majority of the changes being the email-notifier needing to filter messages before sending. Basically, the existing Notify function was wrapped in a loop that goes through the email groups. In order to keep the wrapped code from getting difficult to read, the Notify function was broken into a few smaller functions.