Fixing zoom-slider issue with jumping thumb.

To avoid a circle call of the events change and zoomend a property zooming
was introduced, whichs indicates that the zoom operation was caused by a slider change and
that another setting of the slider value based on the map is not
necessary.
Cleanup code, non-functional.
Change rendering place for map items.

Instead of rendering to the OpenLayers.Map viewport, we render to the
body of the mappanel.
Correct slider layout when rendered to mappanel.
Adjust test for mappanel items.
Correct ZoomSlider behaviour and appearance.

This corrects the behaviour and appearance of the ZoomSlider element when
it is a child of a GeoExt MapPanel.
Merge pull request #191 from marcjansen/zoomslider-fix

Correct OpacitySliders behaviour and appearance.
Merge pull request #190 from chrismayer/fixing-slider-issues

Fixing zoom-slider issues.

Thanks for reviewing @marcjansen