introduced WorksheetGUI, refactored deckpanel

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@26687 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e
removed GeoGebraTube Button

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@26688 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e
refactored DeckPanel


git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@26689 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e