Add missing Internal Links Overview Piktogram
Turn VideoFilesController into FilesController

Allow display of audio tags for audio files for non js.
Lazy Audio Tag Creation

Do not render audio tags in page, which prevent window.onload event in
iOS 8.0.2. Instead create them dynamically from sources parsed from a
json script tag.

Link to separate audio page containing only the audio tag for non js.
Revert iOS 8 window.onload Quick Fix

Now that audio tags are created dynamically, onload is fired
again. Remove special case timeout for iOS 8.
Page Thumbnail Candidates

Turn Page#thumbnail, which hard coded page type names, into generic
Page#thumbnail_file/Page#thumbnail_url which are resolved from a list
of thumbnail candidates defined in the page type.

Allow new file types to be provide thumbnail css rules in entry
specific css file.
Use Thumbnail Candidates in Editor

Resolve page thumbnails just like in the server side case.
Extract Paperclip Styles for Thumbnails into Config

Allow reuse and modification of generated thumbnails.
Add `share` CSS Class to Share Navigation Button

Allows themes to hide the button, if share options are not desired.
Merge branches 'internal-links-piktogram', 'lazy-audio-tag', 'page-thumbnails' and 'share-nav-item-class' into edge