Use the MIME types actually used by the `file` command, which was
recently changed for the detection of the HWPX format [1].
application/hwp+zip -> application/x-hwp+zip
But the HWPX format includes a 'mimetype' file, which contains the
MIME type string "application/hwp+zip", so that was left so because
it may be possible to detect it as "application/hwp+zip".
[1]: ceef7ead3a
Update several references to First Look Media in the code, to better
reflect the current status, where Freedom of the Press Foundation has
taken over the stewardship of the project.
Fixes#343
