Issue/419

This branch allows adds an extra step to the install routine to clone the 'adapt_framework' repository from GitHub.  (Note that in future this could possibly move to a bower package instead)

For each tenant, a copy is made of this repository, and is used to dynamically compile the course, e.g. so that different themes can be used.  In future this could also be used to deliver customised installs.
To save us from adding `git` as a dependency, we could just use the `request` module to fetch a specified release from github - for example https://github.com/adaptlearning/adapt_framework/archive/v1.1.1.zip 

This way we avoid the dependency on git being installed, and we also get a smaller package - the zip should be much smaller than the repo.