+ fixes #0001779: memory leak
+ fixes #0001735: Ellipsoids visibility problems
Draft: Disabled automatic DXF library download - fixes #1785

Note for existing users: Can be reenabled in menu Edit > Preferences >
Import-Export > DXF > Automatic update
+ port Sandbox module to Quarter
+ harmonize API
+ harmonize API
+ support of home path with non-ASCII chars
+ fix more Quarter port issues
+ fix Python binding of 3d viewer