The Disqus comments migration has been initiated. Closes #421
Create DateFields from datetime.date objects rather than ISO-8601 strs

Thanks to Edmund von der Burg for spotting this problem and
suggesting the solution.  This initially worked fine, but since
410f2f99f86c84c9a472185a611e1ae2d0d8e6c6 the __unicode__ method
of ParliamentarySession uses the year attribute of start_date
and end_date.  Although creating the fields with ISO-8601 date
strs is fine from the database's point of view (it's coerced to
a PostgreSQL date correctly) the attribute of the object seems
to remain a string when its printed later in the script.
Add a FIXME about the brokenness of storing the ID rather than a ForeignKey to the model
Add a template-friendly method for returning boundary changes for a Place
Keep the percentage as a float
Display boundary changes on the place_places page
Rename the 'past' / 'future' boundaries to 'next' / 'previous'

This is more accurate, since the 'next' boundaries might
be in the past.
Improve the grammar of statements about boundary changes

This is surprisingly confusing, dealing with the all the
cases where the the session was relative to today, and
when it was relative to the current place's session.
List child places by parliamentary session. Closes #468
A small whitespace change
Display very small boundary changes differently

Typically, there are a couple of very large overlaps between
a constituency and the new constituencies in the next boundary
changes.  There are also other very small overlaps which are
most likely bad data at the edges of the boundaries.  We don't
wnat to elide these completely, however, since even small
changes might be signifcant if they happen to be a deliberate
attempt at gerrymandering.  So, as a compromise, for any
changes of less than 1% we list them separately in a note below
the more significant overlaps.
Merge branch 'show-boundary-changes'

Conflicts:
	mzalendo/core/templates/core/place_places.html
Add n>1 server notes, convert to markdown.

Closes #524
Expires headers, and gzip middleware.

Closes #517
Closes #519