Work with Objects in templates, not JSON

[tmtmtmtm]

Problem

In the templates, we're working with raw JSON a lot. Really we should ensuring that we're properly dogfooding everypolitician-ruby and everypolitician-popolo and operating on objects from those, rather than on raw data.

Proposed Solution

Switch everything to using the functionality that already exists in everypolitician-ruby and everypolitician-popolo, World.rb etc).

Where that functionality is missing, either add it to those libraries, or, if it's not exactly clear how it should work there, or whether it's universally useful, add it initially to everypolitician_extensions.rb instead.

Acceptance Criteria

fgrep \[: **/*.erb | wc -l should return 0 (currently 100).

[tmtmtmtm]

fgrep \[: **/*.erb | wc -l
       0