Support Many Kinds of Projects

[jherdman]

Resolves #381

So, there are two problems with this PR as I see it:

• [ ] I don't have tests for addons
• [ ] I don't have tests for an MU project

I'm a little uncertain how to do this. I have, however, tested this in an addon of my own and can see that it works.

[panthony]

Tried this PR to generate the "pending" for an addon and I encountered an issue where

let moreFiles = this._scanForHbsFiles('tests/dummy/app');

Would return:

[ 'templates/application.hbs' ]

Then later in the processing it would complains about:

ENOENT: no such file or directory, open 'addon/templates/application.hbs'

There are no application.hbs in addon so it looks like it took addon directory as root for templates resolved in tests.

Edit:

This is caused by scanForFiles using a different root than apptRoot and run() appending appRoot to all resolved templates files.