Finish tag post count UI.  Misc tag related fixes

Issue #4683
- Finish setting up pagination in tag management page.
- Add post count warning to delete tag modal.  Fix styling.
- Make sure tag input menu is loading all tags.
- Only include saved tags in tag input suggestion list.
- Unload tag records from store when entering tag route so that
  we get accurate post count.
- Add a resetPagination action to pagination-controller-mixin for
  cases where we want to start fresh.
- Include tag.id when sending tag payload to API.
Fix back button on tag UI page

closes #4703

- previous link used absolute url which fails for subdirectories
Merge pull request #4704 from cobbspur/tagsbutton

Fix back button on tag UI page
Merge pull request #4699 from jaswilli/issue-4683

Finish tag post count UI.  Misc tag related fixes
Adds structured data to first index/tag/author page

closes #4677

- Tests if page is first page or paginated
- Adds relevant structured data to index/tag/author page
- Does not add structured data on paginated pages
- For author structured data, cover image overrides image
- blog cover image is made absolute by image helper
- Tests updated and additional tests for tag and author pages