Added support for optional text label and icon for connection curves

[hasielhassan]

Sharing a small change that i needed to add for a particular implementation of the node editor, not sure if its useful for others but will be great to have it in the main repo.

There are still things that can be worked a little bit more, like the Z position or if some values need to be read from the config or not, I'm open to adjust those if that helps to merge the change.