Blueprint Hooks

[nathanhammond]

We should make it possible for blueprints to support introspecting state and application, and investigate something similar to lifecycle hooks.

This would support things like:

• Conditional addition/deletion/modification of files on ember init.
• Leveraging of custom patching functions during generation.
• Smarter _re_generation.
• Proper generation with different test frameworks as peer dependencies.

...and more.

[rwjblue]

We are working on closing the ember-cli/rfcs repo in favor of using a single central RFC's repo for everything. This was laid out in https://emberjs.github.io/rfcs/0300-rfc-process-update.html.

Sorry for the troubles, but would you mind reviewing to see if this is still something we need, and if so migrating this over to emberjs/rfcs?