Make the news headings slightly larger

To me it looks odd to have the heading the same size as the
text below, and for there to be so little space between them.
Add some CSS comments that should have been committed earlier

For some reason these weren't committed when the corresponding
comments were added to the SCSS.
Make the visited link color of new headings black, not red

As suggested by Martin Wright
Switch the home page view into a class-based view

This is so that in subsequent commits we can localize the
country-specific home page code into each country's app.

This commit also includes some minor reformatting.
Simplify the logic for which "featured person" to display
ZA: Split off the South Africa special case of the home page
NG: Split off the Nigeria special case of the home page
Make a slight simplification to the Nigerian home page code
ZA: the homepage news categories should only be defined in one place

This refactoring avoids repetition in the ZA home template and means
that if we need to change the categories to be displayed that only
needs to be done in one line in pombola/south_africa/views.py
ZA: on the home page, swap "That Week ..." for "Elections 2014"

This is as requested by PMG - fixes #1350
Add tests to check the home page contexts in each variant

These tests can function as smoke tests for the front page, and
check that the elements we expect are present in the context for
core, South Africa and Nigeria.  (These could be extended to check
that the values of those context variables are as expected, based
on the db data, but for the moment this is better than nothing.)