Combine roles

Combined the 3 roles into 1 to make it easier to read/follow

add development task to run `manage.py start` at the end of the app code install. Running `manage.py add_admin` is still a manual process.

Fixed the development and staging tagged tasks to install dev-requirements.txt and tests-requirements.txt. This can be toggled on/off in the vagrant file when testing the appamor profiles.
`dev-requirements = securedrop-requirements.txt + test-requirements.txt`. How about we get rid of test-requirements.txt and just install dev-requirements.txt?