Add spacers to Chat & Nick Lists settings page

Add horizontal and vertical spacers to Use Custom Colors and
Custom Nick List toggles on Chat & Nick Lists settings page.  Adjust
the grid layout to maintain similar spacing as prior.

This keeps it from stretching across the entire screen when the
settings dialog is very wide (e.g. maximized).

Resolves GH-232.

(cherry picked from commit 84c1954b281f42c9915c6a20861269d4121da660)