Refactor mailer and add connection test

[taylortom]

Fixes #2072.

TODO: needs to be integrated with the new dependency checks once they're in.

[lc-thomasberger]

Will this allow us to send different templates with the mailer?

[taylortom]

That should be possible already (but I've added a few related fixes to this). It should be possible by adding your templates to lib/templates, then referencing this like:

app.mailer.send('[email protected]', 'Subject', 'Body', { name: 'path/to/template.hbs' }, callback);

You can also add extra bits of dynamic data to the 4th param, and reference this in your template (we should maybe change this, so that these can be added directly to the template options):

{ 
  name: 'path/to/template.hbs', 
  hello: 'world' 
}

<p class="text">
  Hello {{{templateData.hello}}}
</p>

[tomgreenfield]

Optional?

[lc-thomasberger]

tested with gmail