Update master branch to use 4.2.

• src/core/esriLoader.js and test/unit/core/esriLoader.spec.js default to 4.2

• docs site index.html to 4.2

• maybe return the popup example to the docs pages (see how it was still a problem at 4.1, and see the release notes where it may have been fixed)

• update existing samples based on 4.2 official sample changes

• update README

  • quick start code

  • dependencies table should look like this after cutting new release v1.2.0:

    angular-esri-map	Angular	ArcGIS API for JavaScript	Notes
    v1.0	v1.3+	v3.12+
    v1.1	v1.3+	v3.15+
    v2.0+	v1.3+	v4.0+

• update CHANGELOG