Introduce "Quick Docs" command and extensibility point, similar but parallel
to Quick Edit; and Web Platform Docs provider for that extension point,
based on original prototype at https://github.com/awgreenblatt/InlineWPD.
Change Quick Docs shortcut after discussion with Adam
Merge remote-tracking branch 'origin/master' into pflynn/quick-docs-api

* origin/master: (28 commits)
  updated package validator based on comments in #3437
  remove spurious IntelliJ files
  Updated by ALF automation.
  Another round of code review changes.
  Move HTML templates to htmlContent
  Tweaked dialog so it's centered a little better
  Renamed ExtensionMgr to ExtensionManager
  Code review fixes.
  Update comments to remove the Mustache note, since these can work with Handlebars too
  Make JSHint happy.
  Respond to review comments
  Initial extension manager dialog/view/model (with non-final layout)
  Move out hover preview menu item label to strings.js for localization. Remove unused variables and clean up some variable declarations.
  Merging Glenn's Hover Preview extension into core.
  Only allow leading numbers and letters (largely to prevent names like "..")
  import rewire to assist in testing
  Update Getting started screenshot for 'de' locale
  Fix DISALLOWED_WORDS placeholder in 'de' locale
  Updated by ALF automation.
  'de' locale: Fix Travis build errors (duplicate strings), minor wording edits
  ...
* XD design for Quick Docs, including quiet scrollbars
* Simplify InlineDocsViewer by not overriding load()
Add license info for Web Platform Docs content & logo
Code review changes:
* Update inline widget height when horizontal resizing causes word wrap to
shift around
* Show full URL on link tooltips
* Remove unneeded timeout in onAdded() which was copied from
InlineImageViewer (where it seems to just be a hack for image load timing)
* Remove unneeded check for spaces in URLs
* Fix missing 'return null'
Code review: use LESS vars for text colors; ensure URL tooltip on *all*
links; remove redundant bind() call
Merge pull request #3449 from adobe/pflynn/quick-docs-api

Initial Quick Docs implementation