Add grouping for "Outrigger" containers

[grayside]

While most containers are grouped by docker-compose project, we can create a secondary group based on the label assignment com.dnsdock.image == 'outrigger'.

This would help communicate that the outrigger containers are a bit special, instead of being grouped with the isolated containers which are often less significant.

[febbraro]

This should be pretty easy to do

[febbraro]

we can even give the sync containers a special label just for this. outrigger.category=sync or something like that