Improve error messages on small/large GIS features

[abyrd]

When uploading a shapefile, users may encounter errors like:
"Unable to create opportunity dataset. java.lang.IllegalArgumentException: Feature geometry is too small at com.conveyal.r5.analyst.Grid.getPixelWeights(Grid.java:171)"

Although we do want to avoid processing such tiny features (especially if their near-zero areas end up in denominators) such features can appear in normal data preparation when an original data set is cropped to a study area. Such messages should be demoted to warnings if the error handling code at this point in the backend allows it, otherwise the message should be extended to explain the likely cause to the uploader.