Speedup move_article task

[durden]

Currently the tasks.move_article task does a lot of git command-line actions to manually move an article directory from one publish status to another. This is necessary since this kind of action is not available from the API. However, the task clones the entire content repo each time, which could be improved to speed the task up.

[durden]

We cannot always depend on a local clone of the content repo to be available since we're currently running on Heroku where the local file system can disappear out from under us. However, we could use a specific directory on the local file system instead of a temporary directory as we do now. It might work like the following:

• Check for local clone in a specific location
• If that location exists, cd into it and run a git pull origin master to update it then continue on
• If it doesn't exist do as we do now and run git clone