feat(context-pad); apply background color + remove interaction rect
feat(context-pad); apply background color + remove interaction rect

This commit makes context-pad entries more visible by applying a default
semi-transparent background to them.

It also removes the context-pads interaction rect and allows a user to interact
with elements under the invisible context-pad parts.

bpmn-io/diagram-js,pedesen/diagram-js,thr0w/diagram-js,thr0w/diagram-js,pedesen/diagram-js,tsneed290/diagram-js,chudaol/diagram-js,tsneed290/diagram-js