Redirect to the current path after login [#13]

Upgraded flask-openid in the midst of debugging; the new wersion has
some security fixes so it stays.

Using g.user in layout.html.jinja instead of a local user variable
determines logged-in-ness correctly for all routes, regardless of
whether they pass in a user variable.
Use g.user in all templates, not a local user var

This just avoids an obnoxious class of problems where the user is
correctly logged in, but the controller forgot to tell the template.