fixed issue #17 and introduced MultiView::resetAllViews method

. in the case that several render windows are open and at some points
a different mesh is loaded, the module developer can now not only
update the 'current' (active) render window but all active render windows
via the 'resetAllViews' method

. when a new render window is added, the current grid is visualized in
solid mode
fixed issue #18: switching between: solid, segment ids, quantities works now