WIP: (Mostly) working polling directive

Example implementation on city/region upload page

This is here to get some initial feedback on implementation, thoughts on ways to improve before I finish this up and implement it on the other pages tomorrow. Please comment!
Hmm, might be a bit unclear, but this block is the one that gets called if the is_valid property on the upload object is false. So this indicates an error with the dataset as it is being processed. Things like "upload not a zip file" or "zip file does not contain one shapefile", etc.