fix bugs spotted on intial commit

- [ ] LinksMixin https://github.com/incuna/feincms-pages-api/commit/e3d59acbe98f06b5705aa26150e822d4abfa690b#commitcomment-5408917
- [ ] pass `request` to `reverse` https://github.com/incuna/feincms-pages-api/commit/e3d59acbe98f06b5705aa26150e822d4abfa690b#commitcomment-5408988