Refactor buildout

See merge request !250

Web fixes

See merge request !249

With python 3 we get bytes, ensure we are working on strings.

Make it properties like for other models

If the input is of binary type, returns the decoded version.

Python 3 has brought several modifications regarding sorting.
This patch refactors the code so it can be properly used with
both versions of Python.

This property already provides the declaration in a
suitable form.

We are receiving JSON data for the fork_of field so this
simplifies its handling.

This allows the PlotterParameterCreationSerializer to properly
handle the json given as data parameter.

Better handling of "default". The current code didn't properly
handled absence of defaults.

The FullPlotterSerializer created within FullPlotterParameterSerializer
was not getting any context so it could not perform proper checks
regarding the user that made the request.

Work now on copy of QueryObject as recommended in the Django
documentation and replace the original with the copy

Handle empty choice case for string field

See merge request !248

String fields should provide all the possible values that
a user can select. But if for some reason the field is missing,
the interface loading will break. This patch fixes that by
setting the default value as only choice.

Add django command to get users active on the site

See merge request !247

This commands allows to retrieve the list of users who have a
session opened on the site. Note that this does not mean that they
are currently using the web site, just that they have logged in.

This can be useful when needing to do an unplanned reboot of the
platform for security reasons to warn potentially affected users.

Fix handling of itertools.izip

See merge request !246

In python 3, izip became zip in the global space.

Fix anchors doc

See merge request !245

Various fixes

See merge request !243

This avoids the need to build the psycopg2 packages and thus requires
PostgreSQL dependencies.

The latest version of the sort method requires a key parameter.

Py3 compatibility

See merge request !242

It's not used anywhere in the code.