VueLayers loads select-icon before onSelect function is called

[JoshuaMoelans]

When clicking on a marker, the previous icon is still being used for the first 0.5s after clicking. This is noticeable when changing between a smartphone and a regular tracker. Maybe there is a way to more rapidly change the image, but doing it in onSelect in VueLayerMap is not working.

Follows #101

[JoshuaMoelans]

@BenJStoffels had an idea to fix this, by preloading both styles, and using a V-if to check if the selected icon is a phone or tracker.

Will test this out after the demo day 😁