Better Schema Feedback

[AstraLuma]

When writing a schema file, the feedback you get is pretty vague (from gt):

Error on import gadget
Error: USBG_ERROR_MISSING_TAG : One of mandatory tags is missing.

It gives no indication of what tag it's expecting or where it's looking for it, leaving me to kinda just guess and hope for the best.

[pabs3]

@AstraLuma if you grep the code for USBG_ERROR_MISSING_TAG, you will see there are a number of different ways this error message can be set. In summary it could be interface, type, function, instance, lang, name, id and possibly some more. The code probably needs adapting to pass through the particular mandatory tag that is missing. We would welcome help with that.