Draft: MQ Device for Eventbuilder Monitoring

Added a second output channel to CbmDevBuildEvents through which a second instance of the message which carries the constructed events is sent. This channel is currently configured to run in "pub" mode.

Added a new class CbmDevBuildEventsMonitor, which receives this new message. It then constructs histograms containing "tTrigger - tDigi", once for all subsystems and then for each subsystem individually. These histograms are sent to the histogramm server.

Open issues:

• Right now, the serialization is run twice, as it apparently is not possible to copy FairMQParts objects. This is inefficient and can perhaps be improved.
• The histogramm server can receive configuration data for histograms and canvases it receives. These are sent through a std::string which is set in InitHistoContainers() for each histogram and canvas. Currently these are empty. Probably a folder name should be added here.

@p.-a.loizeau Can you comment on the above issues?

Also: So far, it has only been tested that the histogram server receives messages, but the output has not been inspected in a web browser.

@v.friese @f.uhlig

On edit: Both issues above have been addressed. The output is copied message-wise, which is very fast. Removing the WIP flag, as I expect things to work as they should now.

@p.-a.loizeau Could you remind me how I can log into the histogram server from a web browser? I still would like to test this.