meta-agl-demo: use HTML5 homescreen+background+launcher in HTML5 demo

meta-agl-demo: use HTML5 homescreen+background+launcher in HTML5 demo

Adapt to use again html5-homescreen and html5-background:
* Added html5-background and html5-homescreen.
* Now only html5-homescreen is launched from systemd, while
html5-launcher and html5-background are launched from html5-homescreen
logic.
* Use landscape weston configuration as expected in HTML5 demo.
* Pass --agl-shell-appid=homescreen to WebAppMgr script so it knows
which application implements the UI of agl_shell wayland protocol.

chromium: bc1410d..fa99cf3344
fa99cf3344 [op][agl][wayland] Activate applications when requested from applaunchd
ab1a4cf05d [op][agl][injection] AGL D-Bus implementation of PAL appservice
e5f6143e55 [op][agl][injection] Add application service injection

wam: b0c1e46..8dd3f17
8dd3f17 [op][agl][wayland] Remove unused role code.
defc5af [op][agl][wayland] Fix: do not ignore Panel shell surface type.
6683b08 [op][agl][wayland] Set AGL application ID in all cases
0bb9814 [op][agl][wayland] Properly adapt dimensions for web apps using panel
9af0d23 [op][agl][wayland] Properly pass surface size, type and edge to chromium
e6df86b [op][agl][injection] Declare in web app XML the required injections

Bug-AGL: SPEC-4250
Change-Id: Ie1b1181f3a67ea2ada1912db53e360178a4cf443
Signed-off-by: Jose Dapena Paz <jdapena@igalia.com>