Add support for callouts

[phase1geo]

1- Callout as a visual component to allow for a better understanding of mind maps. It will contain eg: "it's important" or "critical" or "don't forget this", etc. Where sometimes the node contains certain information, and you want to add a visual content as a clarification to it and not as an internal content that will be good to add as a textbox, this element is attached to and clung to the place where it was attached first and always follows so that no confusion occurs during changing the display of the map. The component will also help solve the enhancement addressed here #81