Restful refactor of accounts/ routes (#2133)

* 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.

app/views/accounts/_follow_grid.html.haml

@@ -0,0 +1,7 @@
+.accounts-grid
+  - if accounts.empty?
+    = render partial: 'accounts/nothing_here'
+  - else
+    = render partial: 'accounts/grid_card', collection: accounts, as: :account, cached: true
+
+= paginate accounts