Unmaintained Batch Update Tags 1.1

- Fixed "$forum returns FALSE" error.
- Tested on XenForo 1.5 Stable version.

Features updated:
- Remove all existing tags from selected threads.
- Replace all existing tags with new tags.
- Remove some tags from selected threads.
- Add new tags to selected threads.

Thank you all for the suggestions.

- Fixed thread_list template issue.
- Add new option to remove tags instead of updating/adding.