While file content (MIME) check already existed, the lack of file
extension check allowed arbitrary extensions to be uploaded and
then accessed via the static file server. For instance, a .html file
with JPG content intersperesed with Javascript.
This commit adds a file extension check on top of the MIME type check.
Lists, campaigns, and subscribers tables now support server-side
sorting from the UI. This significantly changes the internal
queries from prepared to string interpolated to support dynamic
sort params.
