Create Transactional Email templates

[aaronjudd]

Create Transactional Email templates as defined in #423

These templates are:

Template Event	Template Type	Implementation Status
New shop admin invite	Basic Text Template	Shop owner inviting another admin to the account (with various levels of permissions)
Welcome (shopper)	Basic Text Template	Shopper registers at shop and receives welcome email (checkbox at checkout to register for this email)
Change PW/Password Reset (shopper)	Basic Text Template
Order canceled	Order Confirmation (variation)
Order confirmation (shopper)	Order Confirmation
Order refund	Order Confirmation (variation)
Shipment notification (shopper)	Order Confirmation (variation)
Subscription Activation		Not yet
Recurring Charge Confirmation		Not yet
Upcoming Charge		Not yet
Charge declined	Basic Text Template
Card Expired		Not yet
Subscription Cancellation		Not yet
Out of stock	Basic Text Template	Not yet
Refunds	Same as order refund above?
Abandoned Cart		Not Yet

The template type should define which variables are expected to be available for use in the template.

[brent-hoover]

All email templates should create emails which display properly in Gmail / Outlook as described in #1059

[brent-hoover]

This ticket also includes ensuring that the email is sent at the appropriate time. A lot of that should already be happening but we should verify.

[kieckhafer]

All email templates are created in #1585