Make the UI responsive

Hiya

Not sure the upgrade of bootstrap is necessary, but doesn't seem to do any harm.

The navbar is now responsive.  The fields resize with the window size.  I also removed the "Server" label, as it was self-evident, and reordered the fields to read more like a `curl` request.  The `help` and `history` buttons still wrap underneath on smaller window sizes, but I don't think that's too much of a problem.

I tried to get the editor resizable, but chrome won't let you resize to less than the original size, so that's pretty pointless. Instead, I made the pane-widths percentages, so they resize with the browser.  One possibility is to add an "Editor width" field in the `#editor_actions` div which allows you to enter a percentage.