feat(plugin): rewrite plug-in to use per file stubs

This commit rewrites the inner workings on the plug-in. As a first
change, it relies soley on `watchify` for watching a file bundle.

Some major rework has been done on how preprocessor and framework
work together:

the framework

* adds a browserify bundle file that contains
the whole project files, including test files

the preprocessor

* creates a single browserify bundle and adds files to it as they
are preprocessed

* invokes browserify to create the bundle and write it to the bundle
file once all preprocessed files have been logged

* after the initial bundle is created, a small stub is published
for all required test files that simply requires these files