Use symbols instead of constants for behaviours

This way we can be more flexible about the factory we can pass as
parameter.

spec/features/budgets/investments_spec.rb

@@ -14,7 +14,7 @@ describe "Budget Investments" do
                   "budget_investment_path"
 
   context "Concerns" do
-    it_behaves_like "notifiable in-app", Budget::Investment
+    it_behaves_like "notifiable in-app", :budget_investment
     it_behaves_like "relationable", Budget::Investment
     it_behaves_like "remotely_translatable",
                     :budget_investment,

spec/features/comments/legislation_questions_spec.rb

@@ -8,7 +8,7 @@ describe "Commenting legislation questions" do
   let(:legislation_question) { create :legislation_question, process: process }
 
   context "Concerns" do
-    it_behaves_like "notifiable in-app", Legislation::Question
+    it_behaves_like "notifiable in-app", :legislation_question
   end
 
   scenario "Index" do

spec/features/debates_spec.rb

@@ -9,7 +9,7 @@ describe "Debates" do
   end
 
   context "Concerns" do
-    it_behaves_like "notifiable in-app", Debate
+    it_behaves_like "notifiable in-app", :debate
     it_behaves_like "relationable", Debate
     it_behaves_like "remotely_translatable",
                     :debate,

spec/features/legislation/proposals_spec.rb

@@ -8,7 +8,7 @@ describe "Legislation Proposals" do
   let(:proposal) { create(:legislation_proposal) }
 
   context "Concerns" do
-    it_behaves_like "notifiable in-app", Legislation::Proposal
+    it_behaves_like "notifiable in-app", :legislation_proposal
   end
 
   scenario "Only one menu element has 'active' CSS selector" do

spec/features/polls/polls_spec.rb

@@ -3,7 +3,7 @@ require "rails_helper"
 describe "Polls" do
 
   context "Concerns" do
-    it_behaves_like "notifiable in-app", Poll
+    it_behaves_like "notifiable in-app", :poll
   end
 
   context "#index" do

spec/features/proposals_spec.rb

@@ -13,7 +13,7 @@ describe "Proposals" do
   end
 
   context "Concerns" do
-    it_behaves_like "notifiable in-app", Proposal
+    it_behaves_like "notifiable in-app", :proposal
     it_behaves_like "relationable", Proposal
     it_behaves_like "remotely_translatable",
                     :proposal,

spec/shared/features/notifiable_in_app.rb

@@ -1,7 +1,7 @@
-shared_examples "notifiable in-app" do |described_class|
+shared_examples "notifiable in-app" do |factory_name|
 
   let(:author) { create(:user, :verified) }
-  let!(:notifiable) { create(model_name(described_class), author: author) }
+  let!(:notifiable) { create(factory_name, author: author) }
 
   scenario "Notification icon is shown" do
     create(:notification, notifiable: notifiable, user: author)