[meta] Essential UX cleanup of Quick Edit

This is *not* only visual change. cfr. the latency points.

I also added this one:

Use D8 core's dialog/modal instead of Edit's own: #1872296: Edit should use core-provided Dialog (instead of its own)

Added #1872296.

Updated issue summary.

Thanks! However, #2004284: Integrate "text formats selector" into CKEditor toolbar is hardly related to in-place editing, it's a WYSIWYG thing. That would really belong in a "essential UX cleanup of CKEditor" issue… :) It's fine to keep it here for now though, I'll move it over once we have such an issue.

That being said, we've already solved/closed #1877044: Edit module's JS gets loaded even on admin pages and #1872264: Minimize metadata HTTP requests triggered by Edit's JS by now.

Updated issue summary.

Update 1: lazy loading as much as possible is impossible without something like AMD in Drupal core, see issue summary.

Update 2: #1872264: Minimize metadata HTTP requests triggered by Edit's JS is implemented by http://drupal.org/project/edit_metadata_cache, but needs two core patches: on #2005644: Use client-side cache tags & caching to eliminate 1 HTTP requests/page for in-place editing metadata, introduce drupalSettings.user.permissionsHash & #1980744-5: Turn edit/metadata into a JsonResponse again, to allow contrib to implement client-side caching of metadata.

Update 3: #1677662: Preload forms to reduce perceived latency to zero is now also closed, similar reasons as #1872264: Minimize metadata HTTP requests triggered by Edit's JS.

Updated issue summary.

Added #1993894: Contextual quick edit toggle should be a <a role="button"> not a <a> because it tracks on/off state.

Updated issue summary.

Added #2080217: Polish entity toolbar visually.

Updated issue summary.