Bug 6874: [QA Follow-up] Last adjustments for future developments

Bug 6874: [QA Follow-up] Last adjustments for future developments

This patch does:

[1] Some trivial template changes. Modified some comments (POD lines).
[2] Converted plugin to new style.
[3] Table updates: renames id to hashvalue, adds a autoincrement id,
    adds filesize, timestamp, owner and category.
    RM: This db rev is in a separate sql file in atomicupdate.
[4] Code references to computed hash renamed to hashvalue instead of id.
[5] Removed some code pertaining to exposing upload dir structure. The user
    now may choose a category; the uploader takes care of storage.
    The list of upload categories is now taken from authorised values; this
    might become a separate table in the future. (If there are none,
    the upload process creates one default fallback.)
    We can add e.g. permissions later, subdir structure, etc. (So dir will
    not necessarily be category anymore.)

Test plan:
[1] Run the db revision.
[2] Upload new file. Check the record in the table. Delete it again; check.
[3] Run t/db../UploadedFiles.t.
[4] Run t/db../FrameworkPlugins.t -incl cataloguing/value_builder/upload.pl

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Tomas Cohen Arazi <tomascohen@unc.edu.ar>