Provide feedback to the user when the data provided is incompatible with the graph

### Background
Some graph types require datasets that are incompatible with other graph types.
A query to get data for a line graph probably won't work with a single stat.

If this happens, we want to alert the user at the lowest level possible. It's possible the ideal level to do this is giraffe, but it's also possible that giraffe isn't the right place.

Start by examining how giraffe receives graph datasets and where graph-type compatibility is currently determined. Identify the lowest appropriate layer for detecting incompatible data and define the user feedback behavior there. Done means incompatible datasets produce a clear alert rather than failing silently or rendering incorrectly.

Written by the indexing model from the issue text.