Expose submissions limit error sooner

Currently, there is a limit of 10 submissions per day. If you reach that limit, you are not informed of the limit until you click the final Submit button on the 11th upload - this leads to some aggravation from time wasted filling out the submission form for the upload that now cannot be submitted. If the error could pop up when the user clicks "upload image" (or whatever type of post) instead of during final submit, I think the experience would be improved.