examples: set crtc/connector properties

[matthoosier-garmin]

The behind-the-scenes manipulation of the per-plane DRM properties
needs to be augmented with some singleton property assignments
too (what CRTC should the connector be driving? what mode should
be used? is the CRC on?).

Also use DRM_MODE_ATOMIC_ALLOW_MODESET in the live commit in
case the new configuration doesn't match with whatever set of
modes and color formats the previous DRM master happened to use.

[codecov-io]

Codecov Report

Merging #33 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master      #33   +/-   ##
=======================================
  Coverage   80.42%   80.42%           
=======================================
  Files           7        7           
  Lines         516      516           
=======================================
  Hits          415      415           
  Misses        101      101

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[matthoosier-garmin]

I haven't been able to test the changes to multi-output and compositor (don't have a machine that has both enough overlays to exercise it and whose driver is new enough to support atomic modesetting).

It works in 'simple' though, and the final mode-setting stuff in the other programs is pretty much the same.