Add cmdeploy "lxc-test" command to run cmdeploy against local containers,
with supplementary lxc-start, lxc-stop and lxc-status subcommands.
See doc/source/lxc.rst for full documentation including prerequisites,
DNS setup, TLS handling, DNS-free testing, and known limitations.
* cleanup: remove CFFI deltachat bindings usage, and consolidate test support with rpc-bindings
major simplification: all chatmail fixtures used in the test are now created inside the cmdeploy plugin,
and do not inherit anything from other fixture machineries, let alone the legacy deltachat CFFI ones.
also fix that pytest report headers show correct chatmail domains under test