Also remove unused migrations test for MySQL.

django-compressor used to trigger processing of the less files during
development. But with the browser-based compiler, an easy replacement is
available. This even lowers the barrier to altering styles, because
getting npm up and running isn't required.

Offline compilation isn't impacted.

Using the most current less version seems to not cause any trouble, so I
removed the version requirement.

Vagrant support was removed from release 1.0. This commit removes mentions of it from the docs.

Closes #1559.

I much prefer just using npm these days.

In our instructions, it wasn't entirely clear that virtualenvwrapper is
required for setup.

Fixes #1088

# Last 5 commit messages
# ----------------------
# 30eead5 Remove custom user app from sandbox [Maik Hoepfel]
# ee3ee02 Drop create_migration.py helper [Maik Hoepfel]
# a77e78c Don't show country field if only one is available [David Winterbottom]
# b5790aa Handle products without a category in GA subission [David Winterbottom]
# 39e0932 Merge pull request #782 from tangentlabs/feature/add_eway_extension_to_docs [David Winterbottom]

Fixes #709

They really don't belong in /contributing.

Building the sandbox was explained in multiple locations, and in
slightly different ways. The sandbox now has a separate document.

They were getting quite long. They've been split up in several
subsections. Some of them are borrowing heavily from the Django docs.