Move JS assets into turbograft folder

Fixes #24 

Moved all JS assets under /turbograft folder. The manifest file now includes all files under the turbograft folder instead of individually including .coffee files in the same folder as the manifest. This should prevent any file name conflicts.

Review @qq99 @tylermercier 
I think initializers needs to happen last-ish, so you will need to specify the dependency order between the files.