(re)add optional callback argument to navigator.id.logout(), fixes accidental API breakage in dev - closes #1399

implement navigator.id.experimental.watch().  closes #1354.  closes #134...

group public API into a single object.  updated doumentation.  wordsmithed error output.  move .request() under navigator.id.experimental too.

ensure onready is called at the correct moment (after login/logout observers have been invoked, subsequent to .watch() being called)

invoke 'ready' observer once the communication iframe is set up and has already checked login state if needed.

Replacing the use of Array.prototype.forEach with _.each, which we are guaranteed to have.

Change Password fixes. closes #1388 closes #1389

* Show a tooltip if the passwords are the same.
* Clear old and new passwords if the password is successfully changed.

issue #1388
issue #1389

Install MPL 2.0 license into LICENSE, prefix MPL 2.0 header on remainder of docs/*.md

General documentation/examples proofreading