Warn/error out if no bus defined for a mapping or individual message.
Warn if bus in a mapping is not defined.
Warn if using send_same and send_frequency together.

The behavior when these are both used is unpredictable, and probably not what
you wanted - there's more information in the docs.
Rename initializeSignals to just signals::initialize()
When merging dicts, combine keys that are lists.
Add database name to log message when we can't find a node.