check_source

D2943 by @deadpin

- Removes broken/unused code that would attempt to delete already added easy-lattices
- Allows the creation of multiple easy-lattices in the same scene AND for the same object (incl. support for multiple vertex groups)
- Add scale factor so the user can create lattices smaller/larger than the target mesh
- Add Catmull-Rom option
- Code style (variable naming, UI naming, return values, etc.)
- Support local-view, thanks to @lijenstina