Sort newest to oldest in sitemap files

Closes #4611

Refactored generateXmlFromNodes to pull the urlElements itself from
sorted values in the lookup

Added some checks to existing unit tests to validate ordering.
Added Highlight to Markdown Help
Change user deletion warning to be more explicit.

Issue #4583
- If a user has posts, show the count in the deletion warning.
Merge pull request #4617 from dbalders/markdown

Added Highlight to Markdown Help
Swap button-order on modal dialogs

Issue #4583

- Delete button should be on the right, cancel on the left, for all modal dialogs.
Fix active menu state on settings navigation

closes #4622
- unfocus ActivatingListItem link when clicked
Return computed url with post object

closes #4445

- post model gets permalink format
- post model queries urlPathForPost to return computed url
- url helper modified to use post url
- urlForPost method abolished and replaced where necessary
- updated tests
Add Tag Meta View

Closes #4509, Closes #4615

- Adds meta title & meta description input fields
- Autosaves meta data
- Shows SEO preview (falling back to tag name & description if meta not supplied)
- Adds `type="button"` to delete button (which closes 4651)
Merge pull request #4565 from PaulAdamDavis/tag-meta

Tag Meta Screen
Merge pull request #4616 from jgable/siteMapOrder

Sort newest to oldest in sitemap files
Add support for zip import

fixes #4607

- moves file checks from db and upload API endpoints to api utils
- adds code to accept and then extract a zip and pull out a JSON file
- zip handling requires a lot of dependencies - this needs a good refactor
Tag Cover Images

Closes #4506

Works just like the Post Cover Images (and uses the same component)
Tiny changes to the component ensures that we can reuse it across Ghost
Merge pull request #4529 from cobbspur/permalink

Return computed url with post object
Merge pull request #4623 from vikhyat/unfocus-nav

Fix active menu state on settings navigation
Merge pull request #4621 from graphiclunarkid/issue4583

Swap button order on deleter-user modal
Merge pull request #4626 from ErisDS/issue-4607

Add support for zip import
Labs page bug fixes

- clear import errors on new attempt
- clear posts and tags from store after delete all
Password change MU

closes #4624
- added user_id to password reset request
- hide old password field
- updated changePassword method to check permissions
- updated changePassword method to work without oldPassword
- fixed bug for errors shown as [Object object]
Merge pull request #4630 from ErisDS/labs-bugfixes

Labs page bug fixes
Merge pull request #4628 from sebgie/issue#4624

Password change MU