Generalize the message templating system to support multiple receipts for a workflow

Rationale
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Allow admin the ability to choose from a list of pre-configured message templates that correspond to a workflow to send email.

Implementation
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1. Add a link "New Workflow Message" (admin/messageTemplates?action=add&workflow=1&reset=1) to the System Workflow Messages tab on Administer → Configure → Message Templates.

2. Create "New Workflow Message"

• Add mandatory drop-down form field to this form :

• Field Label = Workflow
• Field Options = civicrm_option_group.label WHERE civicrm_option_group.name LIKE "msg_tpl_workflow_%"

3. Admin should be given an option to choose between multiple message templates for the workflow and also an option "NO Receipt" which does NOT correspond to any of the message templates, hence no mail will be sent.

• Add mandatory drop-down form field to this form :

• Field Label = Receipt Options
• Field Options = civicrm_msg_template.msg_title WHERE civicrm_msg_template.workflow_id corresponds to the form

This logic should potentially be in all the places wherever we trigger emails/receipts, etc.