load client from npm

Note: There's a pretty lame hack in `package.json`. Post install I need to change directory into the client and npm install there too because npm doesn't install dependencies recursively if the dependency is already required at the top level of the dependency tree. Since roots-cms already requires coffee-script, npm doesn't install coffee-script into the roots-cms-client dependency which causes compile to break when starting roots-cms.

See this issue for more details: https://github.com/npm/npm/issues/1341