Catalogtree

I think that this PR is now in a state where it makes sense to merge it into master.

What's done:
- Load Catalogtree based on topic and language
- Loads Catalogtree definition from catalog service
- React on topic changes (reloads tree)
- React on language changes (reloads tree)
- On hover, a preview of the layer will be shown directly in the map (inspired by oteral's wms browser)
- Add/remove layers to/from map by clicking checkbox in tree
- Collaps/Expand catalog tree, initial state reflects data as returned by gaLayers layers definition initially
- Integrated in accordion
- Style more or less resembles what is specified
- Working example

What's not done (to be done in future PR's):
- React on info button (showing metadata -> which service do we use?)
- Keep state of tree on language changes (this will not be easy as we load from server on language changes)
- Probably more styling (didn't test on different browsers)
- Tests
- Once the layer selection component is in place, we need to synchronize with catalogtree component
- other things...

Note:
CatalogService returns layers that are not defined in corresponding layers service. This means that certain layers are not addable from the catalogtree


Below is the original message of Marc
```
This is only to discuss:

There is a basic example in /ltmom/app/src/catalogtree/example/catalogtree.html

- Expandable/collapsible branches
- Configured with a json file (the equivalent service has to be merged  mf-chsdi3/pull/13)
- Opened/closed branch as defined
- I am not very happy with my template: I need two templates (branches/leafs), should I use two directives, or is there a way to use only parts of a template ?
```