Add extra wrap-prevention space

Chrome seems to require 2 extra pixels when zoomed out to 33%.
Minor tweak to logo

The top line is now double-struck to ensure that the top-left corner is
filled in.  This is especially noticeable when zoomed in.
Adjust layout within the top bar

The aim here was to ensure that if the top-bar controls wrap onto two
lines, then SplitsBrowser takes this into account.

This was achieved by floating everything inside it and adding a an empty
div with clear:both after everything else in it.  The clear:both styling
could then go from the main panel.