refs TryGhost/Ghost#6977
- uses npm script's custom options to streamline ember commands
- add preferLocal to shell options to allow running of npm commands
refs #6977
- adds `grunt-contrib-clean` dependency
- adds `grunt clean` task that cleans the same client folders as core's `grunt clean` ready to be used via subgrunt
refs https://github.com/TryGhost/Ghost/pull/7005
- add `grunt init` task that installs `npm` and `bower` dependencies
- allows Ghost to call this task via subgrunt avoiding the need for a global bower install
Austin Burdine
Kevin Ansfield
Austin Burdine