Create task beautify

Beautify is a task (like build and lint) that acts as an umbrella for
several different tasks. In this case it is jsbeautifier for .json
and .js, and prettify for .html. The first two are pre-build, the last
is post-build.
Change assets path in filerev_assets

By manipulating the path so that it is relative to root, it will be
easier to set up whatever helpers Laravel needs to find it, once I get
to that part of the development.