Added correct contextual Meta Titles and Descriptions

closes #2462

- adds conditionals for pagination for index, tags and author pages
- outputs correct meta title and description according to context
- adds further unit testing
Adjust setup and teardown of route tests.

Closes #3856
- No longer call clearData and initData in test setup because
  migration.init is run during Ghost startup.  The unhandled
  error was a result of clearData removing all the tables while
  Ghost was running--there was a timing issue with the oauth middleware
  checking the refreshtokens table when it had just been deleted.
Merge pull request #3863 from jaswilli/issue-3856

Adjust setup and teardown of route tests.
Merge pull request #3861 from cobbspur/metas

Added correct contextual Meta Titles and Descriptions
Show warning dialog if session has ended in editor

Closes #3839
- Display a warning modal in the editor routes if the user
  is logged out due to re-authorization problems.  This provides
  a chance to copy any unsaved content before being sent to the
  signin page to log back in.
Merge pull request #3873 from jaswilli/issue-3839

Show warning dialog if session has ended in editor
allow re-login when authorization fails on editor.edit route