Add icons and contextMenu-delete to sketch block constraints

[Irev-Dev]

Constraints don't have a icon

And the context menu is wrong

Half these don't make sense even if they are disabled, and "delete" which is enable isn't working.

[Irev-Dev]

but should the constraints be in the feature tree at all, or at least in this form?

Should they be in a nested section

[max-mrgrsk]

Can you delete them in sketch directly?