Add internal documentation building via YUIDoc

Run `npm run docs`

Taken directly from Ember.js with minor changes, with exception that
generator will also create HTML docs as well as JSON data. We can fall
back on this until the ember-cli.com site includes this API
documentation.
Add doc signatures for EmberApp

Extremely minimal doc comment blocks. Not yet qualified to complete.
Add documentation about documentation
Fix lookupCommand with multiple addon commands

Previously `lookupCommand` iterated through every addon with commands,
reassigning `addonCommand` for each one. As a result, having multiple
addons with commands installed would clobber lookup of all but the last
addon’s commands.

Now it breaks out of the loop as soon as it finds a matching command.
Merge pull request #2121 from jgwhite/lookup-command-patch

Fix lookupCommand with multiple addon commands
Fix two typos in the ember help generator command output
Add `before` and `after` options to insertIntoFile
Merge pull request #2123 from BastionFennell/master

Fix two typos in the ember help generator command output
Merge pull request #2122 from bantic/add-before-after-options-to-insert-into-file

Add `before` and `after` options to Blueprint#insertIntoFile
Generate pod components within components subdirectory.
Git based app blueprints

Extends `ember new'`s --blueprint option to accept git remotes in
either git@someservice.com:app-blueprint-test.git or
https://someservice.com/trek/app-blueprint-test.git style git remote
urls.
Merge pull request #2103 from trek/git-app-blueprints

WIP: Git based app blueprints
Merge pull request #2130 from kamalaknn/grp-pod-components

Generate pod components within components subdirectory.
Ensure that the app config does not get mutated by addons.
Merge pull request #2133 from rwjblue/ensure-app-config-wins

Ensure that the app config does not get mutated by addons.
[Bugfix] update CSP addon, it works now.
Merge pull request #2136 from stefanpenner/update-csp

[Bugfix] update CSP addon, it works now.
Update broccoli related dependencies.

Does not bring any symlinking, but does improve support in preparation.
Merge pull request #2138 from rwjblue/update-deps

Update broccoli related dependencies.
Bump RSVP version