Fixes #218

Added check in poll card that allows setting the value of
results_enabled flag.

Access to stats/results now is controlled with abilities.

Polls related to proposals will be accessible to the proposal author
like they were administrators.

spec/models/abilities/administrator_spec.rb

@@ -6,6 +6,7 @@ describe Abilities::Administrator do
 
   let(:user) { administrator.user }
   let(:administrator) { create(:administrator) }
+  let(:poll) { create(:poll, :current, stats_enabled: false, results_enabled: false) }
 
   let(:other_user) { create(:user) }
   let(:hidden_user) { create(:user, :hidden) }
@@ -91,6 +92,9 @@ describe Abilities::Administrator do
   it { should_not be_able_to(:destroy, budget_investment_document) }
   it { should be_able_to(:manage, ProposalDashboardAction) }
 
+  it { should be_able_to(:stats, poll) }
+  it { should be_able_to(:results, poll) }
+
   it { is_expected.to be_able_to :manage, AdministratorTask }
   it { is_expected.to be_able_to :manage, administrator_task }
 end