[ENHANCEMENT] Add in-repo-addon generate and destroy support

[trabus]

This PR adds the ability to generate and destroy blueprints inside of in-repo-addons by adding a --in-repo-addon flag to the generate and destroy commands. It also adds support for components as the first blueprint to be able to generate inside an in-repo-addon.

ember generate component foo-bar --in-repo-addon my-addon
or using shorthand:
ember g component foo-bar -in-repo my-addon

This needs some follow up with docs, it would be helpful to know that you can generate blueprints inside in-repo-addons.

[stefanpenner]

LGTM, my only comment is: it makes me slightly un-easy to add many if statements to add this sort of functionality. It would be great if a later refactoring utilized polymorphism instead.

@rwjblue r?

[trabus]

@stefanpenner This is what structures would provide

[stefanpenner]

@stefanpenner This is what structures would provide

👍

[stefanpenner]

kicking appveyor.

[noslouch]

I think this caused a regression to #2329. I'm seeing vim swap and undo history files get swept up in the build process after generating a component using ember generate component foo-bar --in-repo-addon addon-name