make source/lib file location configurable

[eishay]

I would like to try it out in my Play 2.0 project. Namely, I would like to pre-compile the handlebars. Would be great if the location of files could be configurable.

[stefri]

It's definitely on the list to make this plugin more configurable. However, it might take me maybe an additional month because other things are more important at the moment. I'll see maybe I can push it somewhat, otherwise I'm always happy including a pull request :)