Hide empty categories by default

Change configuration default `hide_empty_categories_in_facet_list` to
True, as showing them doesn't work as intended: Categories, which aren't
applicable to the current instance are also shown.
changed download link for build_debian.sh
Use relative URLs by default in development only (As per @nidico's suggestion in #4)
Merge branch 'develop' of github.com:liqd/adhocracy.buildout into develop
Update mr.developer from 1.21 to 1.23
Upgrade supervisor and recipe

supervisor: 3.0a12 -> 3.0b1
collective.recipe.supervisor: 0.17 -> 0.18
Upgrade python-memcache (1.47 -> 1.48)
Upgrade psycopg2 (2.2.2 -> 2.4.5)
Upgrade Pylons (0.9.7 -> 1.0.1) dependencies

Corresponding commit to liqd/adhocracy commit
db63816f1f012d231a838077a314d55e6ba54114
Upgrade diazo (1.0rc4 -> 1.0.3)

And experimental.cssselect (0.1 -> 0.3)
Upgrade mako (0.4.2 -> 0.7.3)
Upgrade fanstatic (0.11.4 -> 0.16)
Upgrade collective.recipe.solrinstance (1.1 -> 3.8)
Remove whitespace
Rename test-port-free to the importable check_port_free.py
Merge branch 'develop' of github.com:liqd/adhocracy.buildout into develop
Add configuration option adhocracy.auth.secret
Bump formencode to 1.2.5 to support <input type=email>
Add checkversions to development buildout

Checkversions allows to quickly find updated versions of dependencies.

Example usage:

bin/checkversions -v -l 0 versions.cfg
Update Solr (3.6.1 -> 3.6.2)