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.