New base shape - curve

[aheadweb]

Hello. In my project, I often use a curve. And it is the basis for complex figures. I have not the most successful example of its implementation. I propose to discuss how best to do it. Then I could open a pull request with a new shape added.

For example сurve manipulation handlers. Need to combine a curve and its handlers into a group?

[aheadweb]

@raminious

[raminious]

Hi @aheadweb
I was away from this project for a while and I need to think about it to figure out what is the best way to implement that