desktop: allow update of tab widget colors at run time

Adding a new virtual function to all of these classes may seem like overkill,
but of course the idea is that likely we'd allow similar changes to all of
them.

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>

desktop-widgets/tab-widgets/TabBase.cpp

@@ -4,3 +4,7 @@
 TabBase::TabBase(QWidget *parent) : QWidget(parent)
 {
 }
+
+void TabBase::updateUi()
+{
+}