image uploads to projects fail silently if image is too big

[fgmart]

It's good that we prevent too-large images from being uploaded.

It would be better if we give an error messsage when rejecting an image.

The error message should include a statement of the max upload size.

There is an existing error message when you try to upload an unsupported file type (e.g. a ".pages" file).

Perhaps that existing code can be re-used to give the error msg.