- Remove unused variable
- Add typing

- Part of the properties panel for every element (like delete and 
duplicate)
- This allows interacting with elements, generating events and inpect 
their usage. Usually this is unwanted since it might interfere with 
dragging the overlay, but sometimes you want to get a feel for the 
element or check it's contents (GeoGebra for example)

..instead of multiple methods doing almost the same stuff.

This way elements can handle their logic themselves without having to
rely on outside utility classes.

Also restructure files in common in a more logical way.

Components with bigger scope are put to the component root, canvas, 
props panle and new-element-panel.