Run commands on a site with the plugin. Fixes #11.
Merge pull request #13 from solidusjs/11-easy-site-commands

Run commands on a site with the plugin. Fixes #11.
Install latest sass and bower when starting site. New -q option to skip installing when starting site. Fixes #9. Fixes #12.
Use a mutex to synchronize the guest access (deadlocks seem to happen otherwise). Fixes #8.