Minor GUI adjustments.

Adjusted width of some Summary Panel columns and added a spacer column
between Round and Total scores (fixed width, not from settings).

Background color for plots are now applied to entire plot, not just the
area between axes.

Added setting to control axis/label/tick color.
Added ability to filter answer queue by question number. (Issue #20)

The answer queue can now be filtered to show only particular question
numbers by right-clicking on the Q# header. This is a per-instance
setting so users can have multiple answer queues open showing different
questions.