remove everything mongoDB-related

There is nothing in src or tests that relates to MongoDb, so there should be
nothing either in the test environment.
Merge pull request #142 from greg0ire/remove_unneeded_deps

remove unneeded dependency
bump branch-alias version
add missing subscriber for the tree trait
add missing sortable mapping
add missing translatable mapping
stop mapping the id

It can't be mapped in the subscriber, which makes the usage of the
library different for the annotation driver users.
continue to map the id, for BC's sake.
warn about the deprecated id mapping