Now there is at least one environment variable that controls
synapse server's behaviour: SYNAPSE_CACHE_FACTOR.
So, it makes sense to make systemd unit file to use
environment configuration file that can set this variable's value.

Signed-off-by: Oleg Girko <ol@infoserver.lv>

It turned out that merely configuring the root logger is not enough for
"catch-all" semantics. The logging subsystem also needs to be told not
to disable existing loggers (so that their messages will get propagated
to handlers up the logging hierarchy, not just silently discarded).

Signed-off-by: Ivan Shapovalov <intelfx100@gmail.com>

The added logger configuration (--log-config or log_config:) uses
systemd's python bindings to pass messages directly to the journal.

Signed-off-by: Ivan Shapovalov <intelfx100@gmail.com>