Add mimetype application/x-lmdb

Since it shares the *.mdb extension with msaccess,
added a tes file for msaccess, and gave a higher weight
to the msaccess glob for compatibility reasons (so that filename-only
matching of *.mdb still says msaccess).

Reference for the extensions:
Reference for the magic:

Fixes: #168
1 job for work/dfaure/lmdb in 1 minute and 16 seconds (queued for 1 second)