Refactoring file saving

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@28243 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e
#232 safe redefinition of dependent cas cells from input bar

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@28244 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e
Do not redownload Tube file when switching WorksheetGUI -> TabletGUI

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@28245 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e