Stunner - Create Escalation Events Sprite Icons

1) Same as it was required for the conditional events we'll need the icons corresponding to the Escalation events to be added to the the bpmn-icons-sprite.png file.

Note that for the Escalation events four icons are required:
StartEscalation icon
IntermediateThrowingEscalation icon
IntermediateCatchingEscalation icon
EndEscalation icon.

(signal event can be used as reference since it's one of the events that also has the four icons)

In the attached file I'm adding a screenshot with the shapes corresponding to the four escalation events in case its needed for reference. But we have the shapes already.

2) additionally to the modification of the bpmn-icons-sprite.png file, the separate .svg version of each individual icon will be much appreciated.