Changed the callback_url regex so that you can have custom schemes such
as myapp: or my-lovely-app: instead of just http and https. This should
help with mobile development where users can authorize with OSM in their
browser and are automatically redirected to the registered app.
Use the oauth-plugin as a gem instead of carrying a local copy.
This also required that commit eff06faf46 be
reverted as it changed the plugin. I don't think the cosmetic improvement
from that patch is worth the hassle of carrying local changes to the plugin.
