Adds stats and audio levels for Safari. Enables the new getStats API for Firefox, that will get rid of the following warning:
'non-maplike pc.getStats access is deprecated, and will be removed in the near future! See http://w3c.github.io/webrtc-pc/#getstats-example for usage.'

* ref(gum): try to reduce complexity of obtainAudioAndVideoPermissions

Even though I walk through the valley of the shadow of death
I will fear no evil... Reduce indenting and repeated calls to
getting desktop streams by creating a promise chain.

* squash: use arrow func

* squash: move constructor support to helper

* squash: put ff into mediastream constructor check

* squash: ff support media stream constructor

MDN states its been supported since 44. ESR is currently
52.

* squash: rename dsoptions, constant defaults

* squash: move comment about missing tracks error handling

* squash: wrap getUserMediaWithConstraints in promise

* squash: split up av funcs

* squash: hey, some tests...are better than no tests?

lib-jitsi-meet does not get polyfilled for es6 methods.
Using Array.prototype.find will cause breakages in older
browsers, like ie11. The quick fix for now is changing
the find call to be a for-loop. The long term fix will
be discussed soon.

* fix: Fixes version comparison.

* fix(BrowserCapabilities): Searching for the correct version from capabilitiesDB.

* fix(BrowserDetection): Remove unnecessary checks.

In order to include browser capabilities in RTCBrowserType I needed to
refactor RTCBrowserType.