Currently re-writing light theme template

This may be invalid with the other UI changes that are coming soon, but currently we've got a copy of the "light" theme's index.1col.html template, which we're customising occasionally [1] - and therefore having to maintain (things like copyright dates etc.). It'd be fine if we were customising small extensible blocks, but we've got a copy of the complete template.

We should either (1) gather all the differences and evaluate whether they are changes worth pushing upstream and removing our own custom version, or (2) stop pretending to use the light theme and update to some new UI (?)

[1] I just added a {% block copyright %} for bug 923633