criteria: match containers without view

[anrdnet]

Closes #4929

Replaces criteria_get_views with criteria_get_containers which can
return containers without views when the criteria only contains
container properties.

[ddevault]

What does i3 do about this?

[anrdnet]

i3 supports this, as can be tested by the following and similar examples:

$ i3-msg 'splitv'
$ xterm &
$ i3-msg 'focus parent; mark test; focus child'
$ i3-msg '[con_mark="test"] focus'

I made this patch because this feature was part of my i3 workflow, and it broke when I moved to sway.

[RedSoxFan]

Just needs a few adjustments.

[RedSoxFan]

Just needs one small change. Other then that, LGTM

[RedSoxFan]

Thanks!