[UX] Update tag count if tag gets deleted via web interface

王权利请求将github/fork/Razer6/fix_tags_count合并到master

Created by: Razer6

What does this MR do?
  1. Updates tag count in header panel if tag gets deleted
  2. Show tags info message, if last tag is deleted
Why was this MR needed?

Currently the tags count stays the same if a tag is deleted. If the last tag is deleted, an empty tag list is shown

合并请求报告