MP voting comparison WIP

#155 Still to do:

- [ ] Check comparisons where one (or both) MPs were tellers
- [x] Check correct ordering of votes (by date)
- [ ] Find the [actual difference](https://github.com/openaustralia/publicwhip/blob/9eef70833c06a56126010ebbf14f8daf3fbbf7ff/rails/app/controllers/members_controller.rb#L95) between "Votes Attended" and "All Votes" for MP comparison in the php
- [ ] Re-enable [these tests](https://github.com/openaustralia/publicwhip/blob/dfb6dbfc4cc02e2a0f03afa117a5d44f228c015e/rails/spec/requests/members_controller_spec.rb#L167) after fixing #150
- [ ] See if "show all" mode applies to vote comparisons
I don't think knowledge of how the parameters are passed in the urls should belong in the model. It's far from ideal the way it is here in the controller but at least it's explicit. If it were to belong anywhere it should probably be refactored to a plain ruby class.