QmlDesigner.PropertyEditor: Use ToolTipArea in ButtonRowButton

Change-Id: I462f45dd962f1f136e2cf010b0092457345ec485
Reviewed-by: Tim Jenssen <tim.jenssen@digia.com>
Reviewed-by: Marco Bubke <marco.bubke@digia.com>
QmlDesigner.PropertyEditor: Avoid side effects of ColorButton

The ColorButton did change the color as a side effects of rounding error.
With this patch the ColorButton does onyly change the color as a result
of user interaction.

Task-number: QTCREATORBUG-12202
Change-Id: I6504713a27fe7b562b8342229bd287af23156602
Reviewed-by: Marco Bubke <marco.bubke@digia.com>