Issue #97: Add support for specifying multiple email addresses

[djarran]

Description: Implement Issue #97. This allows users to specify multiple email addresses for the action step.

Changes

1. In the step execute function, split emailto value by comma and loop over these values
2. Add loop surrounding existing logic, iterating over the split emailto/recipients array

We did not change the fields available from this step to subsequent steps. There aren't steps that can make use of a comma separated string.

To ensure backwards compatibility, we just make the first email address accessible to subsequent steps.

Testing instructions

1. Install plugin
2. Navigate to admin/tool/trigger/manage.php
3. Click Add new trigger workflow button
4. Enter name
5. Select Assignment: Course module viewed for Event to monitor setting
6. Ensure Workflow active and Realtime processing are enabled
7. Click Add workflow step
8. Select Step type > Action
9. Select Step > Email
10. Enter step name and description
11. Enter multiple emails in the To setting
12. Enter email subject and content
13. Open Mailhog
14. View an assignment activity/module
15. Ensure that emails are sent to both emails

[owenherbert-catalyst]

Hey @djarran I tried to run through this locally but using multiple emails were causing issues in my testing. Can you please take a look?

[owenherbert-catalyst]

@djarran Can you please squash these commits, we should be good to merge then.

[djarran]

@djarran Can you please squash these commits, we should be good to merge then.

Squashed now @owenherbert-catalyst