Add remote display support

Apply a heavily refactored version of the remote display changes from
the CES 2019 demo #3 source demo3/common/agl-service-windowmanager in:

https://git.automotivelinux.org/staging/new-apps

The refactoring of the extracted changes has been done with an eye to
reduce code duplication and minimize the changes to existing code.
As well, the required default policy manager changes missing in the
demo #3 tree have been added to produce a working default policy.

At present the configuration has been hard-coded to assume use of the
tbtnavi application on a Weston remoting display, but testing has
also been done with a second display on one board.  The changes should
not impact operation of any other application, as only applications
with roles listed in the "Remote" layer definition can be displayed
on a configured second Weston screen.

Bug-AGL: SPEC-2914

Signed-off-by: Scott Murray <scott.murray@konsulko.com>
Change-Id: I29380bbbec46969b75ed4fe7e8095db772524082