Try to implement Allan's design

https://bugzilla.gnome.org/show_bug.cgi?id=710125
Improve the new game button
Hide player at move indicator when game is over
Always flip the final result

i.e. remove the unnecessary preference.

This necessitates slightly reordering the preferences dialog.
help: remove visual-results.page

This page describes the flip final results preference, which has been
removed.
Hide the new game button when a game is in progress
Computer: move quickly if only one spot remains

When there's only one spot remaining on the board, it looks silly for
the computer to sit and wait to "think" about it.
Darken the grid

Needed to look good with background color