reply and image count update on deletes

[fatchan]

decide whether to handle reducing these numbers on post or file deletes, since all actions are handled as batches it would b a complex query to update many different threads and reduce the image and reply count

[fatchan]

also currently a bug because a thread would show omitted replies/images with less than 5 replies if one were deleted before then. pushing an update to fix this by not counting omitted posts until there are at least 5. makes more sense either way