Fritz vector layer

LayerGroup defines groups of layers as they appear in the layer-menu. MapService acts as a higher level manager of the layergroups.

Actions
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- [x] Create layergroup factory to abstract layergroup.layers for the rest of the application
- [ ] Url should toggle layergroups on at start or tell Mapservice to instantiate the default layergroups
- [ ] AreaCtrl, PointCtrl, LineCtrl should ask layergroup.getData and not interfere with individual layers anymore
- [ ] Base layer groups, layergroups with an opacity != 1 and temporal layer groups should toggle other layerGroups of the same kind. By the MapService.

- [ ] Create tiled (imp surfaces) and non-tiled (events) vector layers.