[WIP] [feature] UnusedUse - rewrite to use Tokens

UnusedUse - rewrite for use Tokens.
Work in progress

- [X] rewrite to use Tokens
- [X] fix #217
- [X] fix #317
- [X] fix #353
- [ ] set to run after `multiple_use` #480 (when merged!)
- [ ] squash commits
IMO, this should be part of the Config rather than of the fixer:

- some projects may want to fix unused use statements in a folder named ``Fixtures`` if they are not code generation fixtures
- this does not work cross-OS (``strpos`` will not match folders in Windows paths), making it useless