Rearrange & de-duplicate party related templates

- move "MP card" out of templates/member/list.html into a shared template
- use this from both member/list.html and party/mps.html
- create shared party_base.html, use from party/feed.html and party/mps.html
- rename details -> feed, as that is what it is
- restore col-md-half as it got lost in Bootstrap update