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