global: new publication subtype `Proposal`

* Adds `Proposal` subtype to `Publications`.

Signed-off-by: Adrian Pawel Baran <adrian.pawel.baran@cern.ch>
Ah, true. You should use ``inveniomanage upgrader create recipe -r zenodo ...`` to create the upgrade (or simply rename it to ``zenodo_...`` instead of ``base_...`` and then add a dependency on  ``zenodo_2014_03_18_schtask_fix.py`` (see zenodo/base/upgrades/)