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.

spec/controllers/following_accounts_controller_spec.rb

@@ -0,0 +1,14 @@
+require 'rails_helper'
+
+describe FollowingAccountsController do
+  render_views
+  let(:alice) { Fabricate(:account, username: 'alice') }
+
+  describe 'GET #index' do
+    it 'returns http success' do
+      get :index, params: { account_username: alice.username }
+
+      expect(response).to have_http_status(:success)
+    end
+  end
+end