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.).
No, because we still have our own jquery and we require (literally :) to load it and not some other version. And really we shouldn't, because various libraries we use (bootstrap, handson table, jquery-*) modify jquery in-place. This is how jquery's plugin "infrastructure" works. Even in case of embedding bokehjs in bokeh-server there was a conflict, that caused this change, because bokehjs' jquery is modified by prefixed (`bk-bs-`) bootstrap's javascript and server requires vanilla bootstrap's javascript and otherwise you would get a mixture of prefixed and unprefixed classes, events, etc. So now imagine loading bokehjs into notebook and sharing jquery. Nothing would work again. I think we shouldn't take any action on that issue, besides making sure that `noConflict()` works properly in all setups and we don't modify global namespace in any other way.