move new behavior for attach/detach from web to common; various bugfixes

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@35177 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e
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git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@35178 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e