[FEAT] Render signal event

[benjaminParisel]

When you merge your refactoring on the painter, i guess you need to manage conflicts 👀

closes #220
closes #221
closes #401
closes #402

Remaining tasks

• icon position: centered
• BPMN support doc update

[tbouffard]

Rendering with commit c8670ab

It includes a preview of the #404 refactoring. The icon is currently not centered, I have worked with @benjaminParisel on the topic but we currently don't know why the icon is not fully centered (issue on the scaling factor computation? something else?)
The stroke width of the triangle will be managed later

[tbouffard]

Render with 29cb3fd

boundary events

other events

Implementation Notes

We should rework the scaling and origin position computing in the future

• this is a pain to center the icon
• I didn't find a largerratio from parent allowing me center easily the icon, so the icon is small IMHO
• the strokeWidth influences the scaling and makes things worse, so I left it out of the canvas wrapper configuration and set it directly on the mxgraph canvas

[csouchet]

It's normal that the strokeWidth change the ratio from the shape, because MxGraph increase the size of the icon when the stroke width is greater than 1.
So to keep consistency and have the same size of an icon (whatever its stroke width), the ratio from the shape change 😉

[csouchet]

At commit 398e088