The DxfLinePattern creation dialog is finished but not used.
I'm thinking about adding it to line pattern selection dropdown, but that will require to use the newly created one to keep it in the document, as the dropdown doesn't have an access to the document, it only requires a vector of DxfLinePatterns.
A pattern manager window is required to add/edit/remove them.

I continued the work on the spline creation too, as degree implementation is now complete it can now be changed.