Change command run to migrate, start to run

[radiac]

With #10 adding nanodjango serve, the run and start commands become even more unclear.

• Change nanodjango run to nanodjango manage and remove the runserver default. This will then directly mirror manage.py and make more sense to people who know django
• Change nanodjango start to nanodjango run. This is going to be the normal way most people prototyping and sharing files will use nanodjango, so it should be something simple and obvious - run seems clearer than start and less likely to get confused with serve