Update multi-module exporting

Assets are now packaged in webjar format in the project jar.
Exporting between sbt subprojects is via the classpath.
Asset dependencies, whether via internal project dependencies,
configuration dependencies (compile -> test), or external webjar
dependencies, are all extracted as webjars.
Import compile assets directly into test assets
Add metadata to exported assets
Add support for directly importing internal modules
Add method for removing web module dependencies

Can be used to remove assets from the Play reloader classpath.
Helper method for using sbt-web 1.1 with play 2.3.
Merge pull request #82 from pvlugter/new-multi-module

Update multi-module exporting