Ensure we have a git clone of the standards repo on deploy

And that we've created the "working" directory
use unicode literals everywhere
convert tab to spaces
document what we're planning to do
Allow local_settings to set STANDARD_GITHUB_REPO

and add setting for where to find docs in the repo
Start writing way to convert arbitrary markdown docs to html

See the README_CONVERSION.md for what we do.  This commit includes:

* new python packages required for local git manipulation
* deploy script to ensure required directories exist
* code to export commits from the repo
* code to convert the exported markdown into HTML
* a management command to trigger the export to help testing
another note in the README
changes during code review

- improve names
- add some comments
- improve test management command
WIP: start converting views to new repo/cached file backend

still needs work, so this commit will result in a broken site
Initial serving of generated HTML files now working

We look for the file in the directory, and if it exists we embed it in
the template using {% ssi %} - the settings change is required for ssi.

We also make our own dictionaries to hold the tag data needed in the
template, but we make them outside of the view.

The view is now quite a bit smaller as it doesn't get bits and bobs from
the database.

Commit also include various bits of refactoring.
Refactor the redirect views

and fix the broken-ness
Get the main CommitView working

though there are some questions to answer about if we want to commit
them as the StandardView can happily handle both.
Minor context/template updates for commit view to work
Get schema views working with new system

we just use the json files directly from disk in the exported
directories
Delete code that is now unused
Get latest tag directly from git

And remove the LatestVersion model
Fix bug in redirect views
Change to {% include %} from {% ssi %}

- allows us to put django template mark up in the markdown files
- which means we can use the release version in links, generate links ...
- required adding working/html/ to TEMPLATE_DIRS
Properly get the correct initial path for redirects

and get it from the exported directory
Start writing code to generate menus for the files