Add API for retrieving favourites

app/controllers/api/v1/favourites_controller.rb

@@ -0,0 +1,21 @@
+# frozen_string_literal: true
+
+class Api::V1::FavouritesController < ApiController
+  before_action -> { doorkeeper_authorize! :read }
+  before_action :require_user!
+
+  respond_to :json
+
+  def index
+    results   = Favourite.where(account: current_account).paginate_by_max_id(DEFAULT_STATUSES_LIMIT, params[:max_id], params[:since_id])
+    @statuses = cache_collection(Status.where(id: results.map(&:status_id)), Status)
+
+    set_maps(@statuses)
+    set_counters_maps(@statuses)
+
+    next_path = api_v1_favourites_url(max_id: results.last.id)    if results.size == DEFAULT_ACCOUNTS_LIMIT
+    prev_path = api_v1_favourites_url(since_id: results.first.id) unless results.empty?
+
+    set_pagination_headers(next_path, prev_path)
+  end
+end