Feature: Spline point

[Pneumarian]

Describe the new feature you would like to see in Seamly
The ability to add or delete points from a spline would at times be helpful.

I believe deleting would be best served in the Properties dialog, either by

1. having a context menu attached to the item in the list of elements, or
2. by being able to press the "delete" key when the list is active to delete the selected item. In both cases it should probably have a "Are you sure about that?" type dialog.

For adding, I am also seeing two options.

1. In the Properties dialog, have a button at the bottom of the list box of points in the spline. It would read, "Add..." or something like that. I guess a list of possible points to add would be easiest, but I was thinking the dialog would disappear to let one choose the new point(s).
2. The other option would be for the "Add" function to be part of the context menu for the spline itself.

I think these are mostly useful in edge cases, & so probably low priority. Potential problems which I see at this time, involve anachronism, either by irate users being blocked from choosing newer points, or by failing to block anachronism, & crashing.