Allow extension of the Special:Upload form

Allow extension of the Special:Upload form

* Some of the license selection code (License & Licenses)
  has seen some minor refactor to make it more open to
  reuse/extension elsewhere.
  Extension:3D will make use of these for patent selection in
  Iafb1e7e5da4b67f4c5ae7dda511d130ae10f748c
* License/TemplateSelectorLine has been modified so the text
  can be wikitext (as needed for patent labels)
* uploadLicense was renamed to uploadTemplatePreview and
  altered so it can be reused elsewhere. And, like
  window.wgUploadWarningObj, uploadTemplatePreview is now also
  added to `window` so it can be re-used from elsewhere (to
  preview patent templates)

Bug: T182683
Change-Id: I0c097442aa557dd90eb5825553ebf892f9af8a01