Classes used by several BlackLab modules or applications, such as exceptions.
This also includes classes that are also used by e.g. the BlackLab Solr module (solr) or the BlackLab reverse proxy server (proxy), such as WebserviceParameter and WebserviceOperation.
A note about exception classes: maybe modules should eventually get their own module-specific exception classes, although there will likely always be a few shared exceptions such as BLRuntimeException.