Add qbit tag filtering and retag command

[SweetMNM]

Tag filtering lets you filter based on tags and the retag command is like relabel but for qbit tags. Examples added in the readme.

Requires https://github.com/l3uddz/go-qbt/pull/1

[ChuckNorris9939]

See Fork with retag command: https://github.com/SweetMNM/tqm