organisation: use region_slug instead of slug

Rename general slug to region slug to simplify how slugs get
get created. The previous way was an ill thought out version which
caused duplication in database and more problems using them.
organisation: add app hook to show country and regional groups

Attach this app to the main network page and it makes the network
groups accessible on subdomains /<country> and /<country>/<region>

This also removes the role field for network group memberships as
it turned out that was a misunderstanding. A member should have a
title (which describes that member's role, and not both).
organisation: create relationship between network and working groups
organisation: make flags in network group plugin links

Now that we have network group pages we can link to them from our
little flag plugin.
organisation: add network groups to search
Update person search results to include network group membership
organisation: simplify the url for network groups

Use Django's get_absolute_url because the horrible if statements
in the templates are just that... horrible. We still need to keep
two separate urls for country and regional groups because reverse
isn't able to understand conditional keyword argument.
organisation: add comment about extending south's introspection
organisation: add tests for network groups
organisation: added csv export of network groups

Two things to note. For this wee need to add iso3166 and unicodecsv
to the requirements. The standard csv module in python does not
support unicode which is why we need the unicodecsv module to be
able to produce the csv for a global network.

The code which is used to draw up the map of the network groups
located at https://github.com/okfn/localgroupsmap/ has a map where
the countries are keyed according to the alpha3 version of ISO-3166
while django_countries (what we use to offer country support) uses
the alpha2 version. We therefore need to transform our code to the
three letter version.
organisation: added tests for csv output
organisation: add facebook and youtube to network groups views

Facebook and YouTube were added for the csv output but they had
not been added to the network group's page (but they are now and
they are also tested).
organisation: add a test for the flag cms plugin

Conflicts:
	foundation/organisation/tests/test_cms_plugins.py
organisation: reverse import moved

Imports should happen at the top.
organisation: make working and network group model fields consistent

Projects use the form homepage_url (postfix _url) for URLFields. We
need to be consistent in how we name our fields to make it easier
to just use our models in whatever view/template we create.

This also removes a few of CharField null fields since CharFields
in Django are not nullable and will be saved as empty strings. This
changes slightly how the slugs work. We don't have to set them to
None (null) and just work directly from the empty strings.