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
---------
- [x] Create layergroup factory to abstract layergroup.layers for the rest of the application.
- [x] Url should toggle layergroups on at start or tell Mapservice to instantiate the default layergroups.
- [x] Base layer groups, layergroups with an opacity != 1 and temporal layer groups should toggle other layerGroups of the same kind. By the MapService.
- [x] Fix layer menu

Open issues:
- [ ] Animation. Layergroups need to initialise imageoverlays and have a setTemporalLayerToTimeState(). According to behavior configured in the db (rasterInfo).
- [ ] We can download and store vector (events) but not yet draw or do anything non-tiled-vector (fritz)
- [x] Adapt ctrls to new layergroups
docstring