Fix server styles after PR #550

This PR restores  `bokeh-sever`'s look from before PR #550, well approximately, because now `bokeh-server` uses bootstrap 3. Also cleaned up server's templates a bit (more inheritance, etc.).
@hhuuggoo I'm not sure but the contents of `Backbone.sync` here are completely commented out, so it must have moved somewhere? https://github.com/ContinuumIO/bokeh/commit/d4b44c020ba874871719a0b3b2591ccc272810c9 is that commit that transferred all of bokehjs from the old bokehjs repo I would expect history to not be preserved before that.