Make scripts default to mediagoblin_local.ini if exists, mediagoblin.ini otherwise
It's both hard to document and hard to follow to provide commands
where you can specify your own config file, but then you have to
specify that config file every single time for every command
We know people are going to write their own config files... we've
already .gitignore'd paste\_local.ini and mediagoblin\_local.ini.
When no config file is passed in, we should make it so that it
checks for and uses mediagoblin\_local.ini first and if that
doesn't exist uses mediagoblin.ini. This will allow for a simple
way for users to configure mediagoblin and be able to run commands
without accidentally running them on the wrong (non-custom) config
files, and reduce a certain amount of verbage in our docs.