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.).
Almost yes. We have to make sure that all dependencies are AMD wrapped (it looks like handson table is the remaining trouble maker, but that isn't widely used) and we don't do something stupid, like modifying `window`, native types, etc.