Integrate repository id with WMS LayerIdentifier.

Now the extension point adds a layer identifier to WMS Capabilities using the
<repositoryId>:<nativeName>[:<branch/head>] format.

This preserves backwards compatibility with clients that used that information
to get to a given wms layer's entry point in the GeoGig WEB API.
adapt to CommandHook API change
Merge branch 'master' into geogig_ui