cgroup: refactor for cgroups v2, much cleaner + unified hieararchy

Since the cgroups support in Finit is not yet officially released, we
decided to change the back-end to use cgroups v2 instead of the aging
and rather clumsy cgroups v1.  Even this initial refactor is a lot
easier to read and understand, more can still be done since there's
a lot of concepts, data values and the ilk that can now be shared
between different controllers.

Still ToDo: inotify for cgroup.events to clean up leaf nodes, which
            in cgroups v1 was handled by cgreaper.sh.  This is fixed
	    in the next commit in the series.

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

src/Makefile.am

@@ -1,4 +1,4 @@
-EXTRA_DIST         = cgreaper.sh rescue.conf sample.conf
+EXTRA_DIST         = rescue.conf sample.conf
 AM_CPPFLAGS        = -D_XOPEN_SOURCE=600 -D_BSD_SOURCE -D_GNU_SOURCE -D_DEFAULT_SOURCE
 if STATIC
 AM_CPPFLAGS       += -DENABLE_STATIC
@@ -8,7 +8,6 @@ AM_LDFLAGS         = -export-dynamic
 endif
 
 sbin_PROGRAMS      = finit initctl
-pkglibexec_SCRIPTS = cgreaper.sh
 
 finit_pkglibdir      = $(pkglibdir)
 finit_pkglib_SCRIPTS = rescue.conf sample.conf