Structure 'action' template as a ConfirmAction on a HttpActionHandler in an EmailMessage.

Markup the action transactional template as an
[`EmailMessage`](http://schema.org/EmailMessage), containing a
[`HttpActionHandler`](https://developers.google.com/schemas/reference/types/HttpActionHandler)
with a [`ConfirmAction`](http://schema.org/ConfirmAction), giving the template direct
actionability via [Schema Actions](http://blog.schema.org/2014/04/announcing-schemaorg-actions.html).

Markup is in microdata, using chiefly the [schema.org](http://schema.org) schema.

In addition, this implementation uses the `HttpActionHandler` schema component from Gmail's
[Actions in the Inbox](https://developers.google.com/gmail/actions/), which predates and varies
from Schema.org v1.2's implementation of Schema.org Actions. `HttpActionHandler` was introduced in
[Schema.org Actions (Minimal Draft)](http://www.w3.org/wiki/images/7/79/Schema.orgActionsMinimaldraft.pdf)
however it was simplified and changed to appear as [`EntryPoint`](schema.org/EntryPoint) in the released
[Schema.org 1.2](http://lists.w3.org/Archives/Public/public-vocabs/2014Apr/0242.html).