Correctly subclass JingleSession

Remove repetitions

The previous method was clobbering the JingleSession prototype,
preventing the creation of additional subclasses.

Removes fake video tracks from the code

Fix JS error returned by callstats when no error is passed to be reported

Remove browser type check

Depending on the type of browser within which the library is executing,
we take the decision how many times to call getUserMedia (e.g. once for
audio and once for video on Firefox). Upon getting a result of the
call, we used to perform similar browser type checks. I see this as
repetition of logic which makes it difficult to add new browser types
(e.g. React Native). Try to examine the result of the call to
getUserMedia and thus avoid re-checkign the browser type.

Fixes issue with fake streams that are never removed

Nukes the pre-configured bridge from the example config file.

Jicofo is smart and can find any bridge with service discovery and/or
pubsub.

Changes console.* to logger.*

Switch local audio and video tracks when list of available devices changes

Fix JitsiMeetJS option disableAudioLevels

JitsiMeetJS#init accepts an options object in which the property
disableAudioLevels may optionally be defined and is meant to disable RTC
statistics related to audio levels. Unfortunately, the option was used
in a boolean expression which ignored the value of the option and thus
effectively rendered it unused.

Added ability to notify about available media device list changes

Report the error as object to callstats.

Removes fabricSetupFailed.

Adds NWJS to the list of browsers capable of changing the input devices