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 
Hadn't dug into turbograft dependency chain. Happy to hear that it is flat :+1: