Rewrite Pombola's search, and unify multiple search pages

This makes the following changes to search in Pombola:

* There's no longer a separate PU (Polling Unit) search for Nigeria -
  you can just put a PU number into the normal search box.

* Remove the separate Hansard search page for Kenya.

* Adds a set of 'Advanced Search' options that let you restrict you
  search to a particular type of result, and control ordering of
  results.

* Add a "Top Hits" section of the search results to highlight
  (by default) people and blog post matches.

* For South Africa, you can restrict your search results to just
  Questions, Hansard or Committees.
Add styling for the rewritten search interface
Factor out the pagination
Separate out search templates from generic list item templates

(Includes two fixes from Chris Mytton - many thanks.)
made search results displays more consistent
search results with images now display nicely
search results with thumbnails now display nicely on mobiles
Style pagination, remove inactive buttons
Improve the "order by" position and add better results feedback

Chris Mytton did the implementation to wire up the results feedback.
Link to speeches in context in search results

Rather than just linking to the speech page, link to the whole
section that the speech is in.
Add published date to blog posts in search results

This includes SCSS by Martin Wright
Move ordering dropdown back into advanced form

This needs to be inside the advanced form so that when the form is
submitted the new ordering is picked up.

This includes SCSS by Martin Wright.
Fix bug with missing section title
Preserve GET parameters in search pagination

Make sure the advanced search parameters are preserved when the
Next/Previous links are clicked.
Make the text in the search box more generic

The search covers more than just names and parties, so use more generic
text to show that.
Remove places and info pages from ZA search

PMG requested that these items not appear in the search results. The
places are better covered by the rep locator, and the info pages aren't
really what people are likely to be searching for.
In advanced search order hansard and questions by date

Order hansard and questions by date when they are selected, everything
else order by relevance.
Rename Committee to Committee Appearance in advanced search

As requested by PMG.