! Fix invalid thumbnail sizes (per #1294)

Signed-off-by: Peter Spicer <sleeping@myperch.org>
! Fill in MIME types for files that we have but that we don't have information on. Fixes #1294

Signed-off-by: Peter Spicer <sleeping@myperch.org>
! Improved description of the post moderation page, fixes #1280

Signed-off-by: Peter Spicer <sleeping@myperch.org>