General Popolo json import script.

Rewrite and merge the Popolo json import scripts from SayIt Philadelphia
and OpenNorth to make a more general Popolo json import script which
works in an 'upsert' manner.

It should now update any existing entries and associated records, rather
than delete/recreate the identifiers/other names/etc. Also fix a number
of bugs.
Break popolo importer out of management command.

Break the Popolo importer out of the management command so we
can use it from the web frontend too.
Extra requirements for https with SNI.

python-requests needs some extra packages in order to be able to
fetch stuff from an https site with SNI. This is particularly
noticeable now that PopIt uses https.

https://stackoverflow.com/questions/18578439/using-requests-with-tls-doesnt-give-sni-support
Allow setting the instance when importing Popolo data.

In sayit.mysociety.org, we need to be able to choose which
instance to associate speakers with, so allow that as a command
line argument to the sayit_load_speakers management command.
Only import persons.

Currently, persons are the only objects from popolo that sayit
uses, and they are imported as speeches.Speaker objects, which
are popolo.Person objects which are subdomain instance aware.

Rather than making instance aware versions of the other Popolo
object types, for the moment we're going to import only the
Persons.
Popolo importer now works with a single file or unpaginated output.

The popolo importer now works with unpaginated output like
http://scrapers-ruby.herokuapp.com/organizations

Also better support for popit and local file imports.
Basic import people page.

This still requires linking in from elsewhere.
Let the user know how the import went.

Show the number of new speakers imported and the number of speakers
'refreshed', which is what I'm going to call updating speakers
who are already there if they needed it. Better language suggestions
welcome!