House page

[octopusinvitro]

This PR adds a new page class for a legislature.

• Adds a Page::House class and tests
• Adds the route to app.rb (/:country/:house/)
• Adds a new template and tests. The template was taken from the country template which was updated to show information from the house and to remove the loop on legislatures.

[tmtmtmtm]

you shouldn't need to instantiate with both of these. Passing just the house would be cleaner, and the country can trivially be derived from that.

[tmtmtmtm]

There's a lot of duplication now between this template and the country one. Unlike #15245, where the plan is to delete the per-country download page anyway, resolving the issue, I'm much less convinced it's OK here. We'll have two pages that are almost identical and it's going to be very easy to forget to change one when the other changes.

[octopusinvitro]

After rewording the House template, it looks like this:

[tmtmtmtm]

👍 — except we can't merge before #15245, as the pages here have a link to the (not yet existing) download page for the legislature.