add timestamping capabilities

When an experiment is locked, it can now be timestamped with the external
service UniverSign. The ASN-1 token is kept in the uploads/ folder and
its path is in the db. A timestamped experiment cannot be
unlocked/edited.
change type to email; add some doc
add wikilink
remove a lot of the update.php file

This also fixes a bug : an old instruction no longer valid that breaks
the update.
some more update.php modifs
a nice message is always better
add title to images on showXP
add md5sum to uploaded files (if size < 5 Mo)

The md5sum is also displayed in the pdf. This way when you validate the
experiment, you validate the files also :)
timestamped pdf is now kept and displayed for download

This way you can still add comments and not have your experiment failing
the sha sum because of added comments in the generated pdf.
you can now click title to get into item view, and other cosmetic stuff
Merge branch 'next'

* next:
  you can now click title to get into item view, and other cosmetic stuff
  timestamped pdf is now kept and displayed for download
  add md5sum to uploaded files (if size < 5 Mo)
  add title to images on showXP
  a nice message is always better
  some more update.php modifs
  remove a lot of the update.php file
  add wikilink
  change type to email; add some doc
  add timestamping capabilities