Better Error reporting

[gunnarx]

This ticket collects things to improve on error reporting, when the tools get incorrect input.

1. If no Interface is in the YAML, then no output. The D-Bus generator doesn't fail until the XML-reformatting where it says there is no start node (with an ugly exception backtrace).
   Instead, check that an Interface node exists and/or check if generation result is empty, and report it to the user.

2. Related to the above, the current template-driven generators like BAMM, DTDL, and protobuf need to be updated for Interface. They don't fail because they just loop over "all methods in the Namespace", etc. So if there aren't any, the output will be mostly empty. Anyhow, perhaps this could be considered correct behavior for a file without an Interface node, but they should be updated.
   Ultimately, add a check for Interface node, in the generic ifexgen - at least it probably should output a warning.

[gunnarx]

3. When the implementation switched to dacite, it does quite good checking for incorrect IFEX files but the error messages are not always the best. It can create an exception and ugly-backtrace if the input is not right. So the third item to improve is friendly messages with clear reference to the line number (which is lost currently in the YAML -> dictionary -> dataclass conversion.