Allow dropping channel and/or subscriber via unix control socket

[nemanja-boric-sociomantic]

There could be a case when the channel is not needed and the overflow is present, but it should be dropped.
The current solution is to pipe all the overflow from via dmqcli to /dev/null. However, this is just a workaround, since dmqcli is not intended to be use as the administrative application, so it doesn't have this features.

It also brings the problem with the subscribers - dmqcli doesn't currently support subscibers, so there's no way to drain the subscriber based channel.

It seems better, now when we have the unix control socket, just to issue an command and make dmqnode to drop the channel including the overflow.

[Geod24]

Last but not least, dmqnode is not open source :)

[nemanja-boric-sociomantic]

You mean dmqcli, but yeah :-)