Disable guide page when Budget is not accepting

Why:

When there is not Budget accepting (Investment creation) the guide page
doesn't have much sense as it will give the user an option that can't be
used (creating an Investment).

How:

Using `Budget.current&.accepting?` conditional at GuidesHelper to link
to new proposal link instead of guide page, and adding an scenario to
guides feature spec for it.

app/helpers/guides_helper.rb

@@ -1,7 +1,7 @@
 module GuidesHelper
 
   def new_proposal_guide
-    if feature?("guides")
+    if feature?('guides') && Budget.current&.accepting?
       new_guide_path
     else
       new_proposal_path
@@ -9,7 +9,7 @@ module GuidesHelper
   end
 
   def new_budget_investment_guide
-    if feature?("guides")
+    if feature?('guides')
       new_guide_path
     else
       new_budget_investment_path(current_budget)

spec/features/guides_spec.rb

@@ -13,7 +13,8 @@ feature 'Guide the user to create the correct resource' do
     Setting['feature.guides'] = nil
   end
 
-  scenario "Proposal" do
+  context "Proposals" do
+    scenario "Proposal creation" do
       login_as(user)
       visit proposals_path
 
@@ -23,6 +24,17 @@ feature 'Guide the user to create the correct resource' do
       expect(page).to have_current_path(new_proposal_path)
     end
 
+    scenario "Proposal creation when Budget is not accepting" do
+      budget.update_attribute(:phase, :reviewing)
+      login_as(user)
+      visit proposals_path
+
+      click_link "Create a proposal"
+
+      expect(page).to have_current_path(new_proposal_path)
+    end
+  end
+
   scenario "Budget Investment" do
     login_as(user)
     visit budgets_path