Add repo scan when adding repo to be monitored.

Adding a scan during the add_repo() call causes the script to first try
and check the status of the git repo before it is added. This means two
things: the scan will fail if the repo doesn't exist or is the wrong type
and that we start of with repo status info.
Require a repo name when adding repo to be monitored.

We should require a repo name when adding a repo via WP-CLI. The name is
now the first argument, followed by the path to the repo.
Adding `scan_repo` command to scan a specific repo.
Adding list_repos command to Quickstart Dashboard.

Command lists the monitored repos for the user.
Add hooks to repos when monitoring repos.

Now when a repo is added to be monitored we will automatically insert a
hook that will re-scan the repo after it has been updated. In this way if
a user manually updates a repo quickstart dashboard will know about it
right away and stop bugging them.