Allow importing filters from another instance of cibuglog
The goal would be to enable creating a new instance of cibuglog that has all the filters of another instance, and some new ones. This makes sense when filing bugs for a tree based on another one as it removes the need for duplicating filters.
To make this work, we need to have a consistent way of tagging machines (i915-infra#4), and also expose all the filters through a REST API (#50).