Attempt at making it clearer what needs to be done for what kind of
customisation. Created a new topic that lines out the prepatory
steps that need to be taken, and moved duplicate information from the
how-tos into the new topic.
To set a base for upcoming docs changes, the docs directory structure
has been streamlined to follow a simplified version of Django's docs.
The old _draft folder has been removed. Both files from there and the
current docs that don't fit nicely into the new structure are in _old/
for the moment.