Prevent route blueprint adding duplicates

Addresses #1035
Rename integration-test blueprint to acceptance-test

Addresses #1032
Merge pull request #1043 from jgwhite/rename-integration-test-blueprint

Rename integration-test blueprint to acceptance-test
Merge pull request #1042 from jgwhite/route-blueprint-patch

Prevent route blueprint adding duplicates
Add blueprint listing in ember help generate

Refactor help API around `printBasicHelp` and `printDetailedHelp`.

`ember help` uses `printBasicHelp`

`ember help <command-name>` prints basic and detailed help.

Implement `printDetailedHelp` in the generate command to list out
available blueprints, grouped by package.
Add changelog entry
Merge pull request #952 from jgwhite/generate-list

ember help generate
Add missing descriptions for `build`, `serve`, and `test` commands.
Merge pull request #1045 from rjackson/add-more-help-descriptions

Add missing descriptions for `build`, `serve`, and `test` commands.
Keep --output-path up to date from build and serve commands.

* Adds ability to specify output-path for `ember server` command.
* Removes usage of `broccoli-export-tree` in favor of maintaining a
  single set of logic in the `Builder` model. (previously we had logic
  in both the `Build` task and `loadBrocfile` utility function to keep
  the output directory in sync)
Merge pull request #1034 from rjackson/live-output-to-dist

Keep --output-path up to date from build and serve commands.
Check for ember-cli updates and display message to user if an update is available

Add ember update command and change update message to suggest running that rather than npm install

Persist checkForUpdates setting and version information via .ember-cli file

Add .ember-cli files to blueprint tests/fixture directories where needed

Wrap checkForUpdates call/command.validateAndRun() in a Promise to prevent async weirdness

Remove unnecessary ember-cli file (already there)

Make an HTTP call to npm when checking for updates rather than loading npm module

Syntax fix and remove stray call in test to create ember-cli file (not needed)

Add test to confirm update command is run

Update the package.json file manually after doing a global install, so
the correct ember-cli version is reflected there

Add a couple unit tests for update command/update task

fix syntax errors

Remove debug statement

Add entry to CHANGELOG