Bug 444143 - [GTK3] Reset selected background color in Table

When setBackgroundColor is called for Table it results in
a call to gtk_widget_override_background_color with the flag
GTK_STATE_FLAG_NORMAL which overrides the color for selected
items' background despite the flag. Therefore the selected item
color must be reset to the default.

Change-Id: Iab3cad4e01cf87cca04e536fdea8991c818d0336
Signed-off-by: Sami Wagiaalla <swagiaal@redhat.com>
(cherry picked from commit 716d35d30c1f639a04515188fedd89bb3aaf12bc)