Is your feature request related to a problem? Please describe.
First of all, thank you for such a great work on this library. I would like to request a feature that angular-split allows users to have custom icon.

At the moment the icon is using a background-image url

Describe the solution you'd like
I would like angular-split provides a way to customize this, the best is allow using svg.

The current workaround is I override styling from root.