organisation: add a plugin to show network group country flags

This adds a simple plugin which shows only country flags in
standardised dimensions. This plugin could be expaned later to
allow users to better control how to list network groups (i.e.
not only flags).

The flags come from the Open Icon Library and are in public domain
according to them. README from the original collection is included.
Flags were re-exported to png from the svg to ensure standard
dimensions. Some changes were made to the svg versions of a few
flag to allow export area to be the drawing and not the page
(needed for standardised dimensions). Some of the svgs contained
some extra cruft or longer lines outside of the page and therefore
needed the changes. The svgs added in this commit are the modified
ones.

It would also have been possible to use the flags that come with
django-countries but those versions do not fit very well with the
flat design and since we now have svgs we can better control the
size and dimensions.

Conflicts:
	foundation/organisation/cms_plugins.py
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.
Migration fixes
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).
Moving migrations forward
organisation: create relationship between network and working groups
Moving migrations forward
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.
Moving migrations forward
organisation: fix pep8 errors

I really screwed up pep8 in this view didn't I?
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.