This will help a great deal with #9377 when a caching reverse proxy is
configured.

Fix #6856
Fix #6951

* Add routing specs for accounts followers and following actions

* Use more restful route naming for public account follow pages

Moves two actions:
- accounts#followers to accounts/follower_accounts#index
- accounts#following to accounts/following_accounts#index

Adds routing spec to ensure prior URLs are preserved.