desktop_shell.panel_size was only used to determine if sway should
rearrange the output when rendering the panel in the output_pre_render
hook. This is not needed since the output will have been arranged at
that point.
It also caused sway to rearrange all the time when running with two
or more different monitors/resolutions because panel_size kept changing
with every output_pre_render callback.
Should fix #514
Track each panel separately via its wl_resource. `set_panel_position`
might be called before `set_panel`, so reuse panel config.
Place the position in panel_config so that each panel has its own
position.
This does not work as expected. I think the problem is on the wlc side.
Please review, @Cloudef. To reproduce the issues:
1. Run sway
2. Open terminal in sway
3. Run swaybg
swaybg will create a surface and ask to have it set as the background,
but wlc_handle_from_wl_surface_resource will return 0. If the swaybg
surface is a shell surface, then it works - but wlc complains about the
pointer type and segfaults as soon as the pre-render hook tries to draw
the background.
