remove group name from hierarchical tags

Oscar requested to merge the-boy-sebastian/tildes:tag-conv-rm-group-name into master

fully implements #380 by removing the initial tag in a hierarchy from a new topic if it's the same as the topic's group name and removes duplicates

example just to illustrate: if a new topic in ~group has the tags tag,group.tag,group.another tag,unique, this MR will change that into tag,another tag,unique

Edited by Oscar

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