call goBack-method from "back-button" in the header

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@26717 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e
clean code

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@26718 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e
after "open" is clicked - call "goBack" (switch view)

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@26719 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e