Web interface to setup job broker(s)

[sverhoeven]

Broker now has to be put in config file by hand.
When a web app can do this, users don't have to edit the config file or have to have direct access to it.
For some brokers username/password/certificates are required, those should also be able to be configured from the web interface.

This should make it easier when application is distributed for administrators to configure where job should be run.