Offline event in Touch

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@27824 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e
Missing part of last commit

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@27825 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e
Keep cached material previews, simplified BrowseGUI resizing

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@27826 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e
Make sure material panels are invisible until we populate them

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@27827 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e