Breaking: Upgrade MediaElement.js (fixes #298 #297 #232)

[swashbuck]

Fix #298 #297 #232

Breaking

• Upgrades MediaElement.js from v2.21.2 to v7.0.5. This includes breaking namespace changes.
• Removes Flash support
• Removes IE 9/10 support
• Removes Vimeo support (Vimeo-specific styles and JS shims). Anyone who needs Vimeo support should migrate to the Adapt Vimeo plugin.
• Removes YouTube support. Anyone who needs YouTube support should migrate to the Adapt YouTube plugin.

Notable changes and deletions

• First off, refer to the MediaElement migration notes, particularly regarding the namespace changes.
• speed, jumpforward and skipback have moved to mejs plugins. Other plugins can be considered for inclusion in the future.
• The MediaFeatures object is now just Features
• MediaElement success callback passes different parameters: media, node, and instance. I've added documentation about this to onPlayerReady() which is the success callback function.
• Some properties have moved. mediaElement.player changed to mediaElement.options. selectedTrack has moved to the instance object mentioned above.
• Removed many assets. Icon implementation by default now uses SVG symbols. When using the Vanilla theme (PR listed below), these icons are replaced with Vanilla font icons.
• Added a README.md to the libraries directory detailing the changes we've directly made to the mejs library itself. These changes have pending PRs at the mejs GitHub repo.

Fix

• Video Speed menu is not accessible #297
• Cannot navigate caption button language menu with accessibility  #232

Configuration changes to existing courses

None

Dependencies

• Requires Vanilla theme updates from Update: Update Media component styles to support MediaElement.js (fixes #523) adapt-contrib-vanilla#524. The exact Vanilla version is TBD, but we should probably add it to the readme.

Regression testing

The following fixes could use retesting. I could not find the original GitHub tickets for some of these.

1. "Default shortcut keys trap a screen reader user inside the player once in focus. These keys are unnecessary as one may traverse the player in a linear fashion without needing to know or use shortcut keys. Below is the removal of the default shortcut keys." The fix I've implemented is slightly different from the old fix.
2. Removed: "The default seek interval functions are passed two different data types from mejs which they handle incorrectly. One is a duration integer the other is the player object. The default functions error on slider key press and so break accessibility." The old fix rewrites the defaultSeekForwardInterval and defaultSeekBackwardInterval functions to check the type of the input. These two functions have been slightly rewritten in the newer mejs library, so a fix may no longer be needed. I have removed the previous fix for now.
3. Removed setupPlayPauseToggle() fix: "Overrides the default play/pause functionality to stop accidental playing on touch devices... we don't have a this.mediaElement.player ref on iOS devices." The fix seemed to actually break play/pause functionality on iOS, so I've removed it.
4. Removed buildfullscreen() override ("Overwrite mediaelement-and-player buildfullscreen to remove global delete"). The only significant difference in the current override was to remove two delete hideTimeout lines. The new buildfullscreen() in mediaelement-and-player.js does not use this.
5. Removed killContextMenuTimer override to "remove global delete" since it no longer exists in mejs
6. Removed CSS fix for adapt-contrib-media: toggleCaptionsButtonWhenOnlyOne adapt_framework#1883
7. Removed CSS fix for "touch devices to override standard hover event in mep.less L119"
8. Removed CSS fix for "missing control icons on iOS touch devices"
9. Removed CSS fix for "The width set by mejs is always 100% of container, set in pixels. Having a fixed pixel size prevents iOS from changing orientation without scaling."
10. Fix for firefox fullscreen api In Firefox, it's necessary to press Esc twice to completely exit fullscreen #239 The fix for this PR was recent, so it should still be fine.

Known issues

• Fullscreen triggers the inview handler of the components underneath #304

[simondate]

I've noticed that Youtube isn't working either - The README does mention support is temperamental, but perhaps this should be properly documented as being removed like it is with Vimeo.

[swashbuck]

I've noticed that Youtube isn't working either - The README does mention support is temperamental, but perhaps this should be properly documented as being removed like it is with Vimeo.

Thanks, @simondate . I've added this to the PR notes above and have made it more clear in the readme.

[swashbuck]

Ready for review.