Convert xblock-factory into grunt-init template

While the original incarnation of the xblock-factory "worked", its
workflow was less than ideal.

The workflow was based on a fork model, where projects were to be
started by forking the template which would then bootstrap itself into a
customized XBlock. Unfortunately, Github (our primary source host)
doesn't allow a single user/organization to fork a repository multiple
times. While this could be worked around manually with Git (sans "hub"),
it defeated one of the projects original goals. This forking model was
originally envisioned (by me, ugh) to leverage the social/graphing
aspect of Github to track derivative works created with this new
factory/SDK.

Instead, this has now been refactored into a (simpler) grunt-init
template. This template can then be invoked manually on the development
system or as an integrated component of the xblock-sdk Docker container,
which will be released shortly.

TL/DR: Live and learn.
Since this project no longer bootstraps itself, we don't need this.