Remove old maps module

Metabolic map drawing can now be handled entirely by visbio (primarily developed by @zakandrewking), and it does a very good job. I have added an example of this in the documentation included with this pull request.

The old maps module was dependent on a patched version of bigg, which I have running locally on my server, and isn't a good long term solution. Therefore, the internal maps module should be removed, and visbio should be used instead.