Integrate Chromium and WAM recipes.

Integrate Chromium and WAM recipes.

Create a new layer called meta-html5-framework.
It contains the following recipes:
* chromium68 to build the browser shared library and browser code.
* chromium-browser-service for the browser widget.
* wam for the web application manager.
* wam-tinyproxy is a direct dependency of wam.

Defines a new packagegroup, which is added to the agl-demo-platform
image in case agl-html5-framework is configured as a feature.

Bug-AGL: SPEC-1885

Change-Id: I39f01ab09e198cd139e95ff3c784af563b54329b
Signed-off-by: Jacobo Aragunde Pérez <jaragunde@igalia.com>
(cherry picked from commit 19e71462fc44093c6f9046e60c72adeedfca7858)