Promisify all the things and error on player

[squarebracket]

Errors in EME will now fire player.error(). For spec-compliant EME and Safari, it's promises all the way down.

Also cleaned up the handleEncryptedEvent stuff; it was calling requestMediaKeySystemAccess twice for every encrypted.

Added a bunch of tests to test the various error conditions and make sure they spit out the correct error message strings.

A few things to note:

1. I am using player.tech_ as an error event bus for IE11 since it doesn't have promises. Those events are then caught and the error handler is called.
2. The tests will fail on IE11, because promises. I may just do a batch exclude of those tests when running on IE11. (this is the same on master)
3. I do not shim video.msSetMediaKeys when available since it is apparently read-only and thus can't be assigned to in strict mode.
4. I removed the shimming of window.navigator.requestMediaKeySystemAccess in a bunch of tests because I don't think it's necessary now (so long as you're running on localhost). Let me know if you think it should be shimmed out anyway.

[squarebracket]

Bump. Now ready for review.

[squarebracket]

Figured out why the tests weren't passing: I forgot getLicense was getting promisified. Fixed now.

[squarebracket]

I thought my tests would catch problems after rebasing, but they did not -- initializeMediaKeys is causing problems with the error handling, which I will have to fix.

[squarebracket]

I opted to simply automatically fire an error on the player unless the callback explicitly returns false.

[squarebracket]

Changed to use a parameter passed to initializeMediaKeys to suppress errors when possible, and cleaned up the testing code a bit.

[squarebracket]

uh, looks like videojs-generate-karma-config broke?

[squarebracket]

Actually maybe it's a transitive dependency that broke, I can't really tell.

[squarebracket]

Using lts/carbon fixed it.

[squarebracket]

One thing that came up in the process of this PR is that setupSessions is called on every encrypted, which is a bit excessive. I tested with

player.on('loadstart', () => {
  // wipe old sessions when changing sources
  player.eme.sessions = [];
});

and it fires as desired on all browsers. I've got a small diff from this PR to what I'm actually using in our internal player, which has the changes for key rotation, where I am using loadstart.

Is that something I should add to this PR, or keep it for the key rotation PR?

[squarebracket]

Actually, the key rotation PR includes some general cleanup and simplification, so it probably makes sense to just hold it off for that PR.

[gesinger]

I think holding off from this PR makes sense, just to keep changes as isolated as possible.

[misteroneill]

@squarebracket Is this PR depending on the key rotation PR or vice versa?

EDIT: Nevermind, answered question elsewhere.