Update minimap outside of render cycle

[nikku]

What should we do?

The minimap is an auxiliary navigation component that shall not negatively affect the modeling performance. Currently though it updates in sync with core modeling operations, leading to a ~30% penalty if used, independent of whether or not it is visible (or not).

• Minimap shall update asynchronously, outside of render cycle
• Minimap shall only update (affect performance) if currently shown

Why should we do it?

Traced as part of camunda/camunda-modeler#4320 as a big performance impediment.