Add a make target to update the built version of the app on Github pages

This checks out the gh-pages branch in a copy of the repo, copies
the current build to that repo and creates a commit with the changes,
then pushes the result back to the gh-pages branch.
Redirect to an https:// location when accessing the app from a non-localhost host

For security the OAuth login flow requires the redirect URI to be an
HTTPS endpoint. We also want to ensure that the user is receiving the
correct copy of the app.