Add Flash Notices for Failure

When a Task #create or #update operation fails, a flash notice is
presented to the user when the task index page reloads. You can see this
easily by trying to create a new task with the same name as an existing
task.

Additionally, cleaned up controllers to not have unneeded format
blocks.

app/assets/javascripts/application.js

@@ -13,4 +13,5 @@
 //= require jquery
 //= require jquery_ujs
 //= require turbolinks
+//= require bootstrap
 //= require_tree .

app/controllers/tasks_controller.rb

@@ -4,18 +4,22 @@ def index
   end
 
   def create
-    respond_to do |format|
-      @task = Task.new(task_create_params)
-      @task.save
-      format.html { redirect_to tasks_path }
+    @task = Task.new(task_create_params)
+    if @task.save
+      redirect_to tasks_path
+    else
+      flash[:error] = "Task creation failed!"
+      redirect_to tasks_path
     end
   end
 
   def update
-    respond_to do |format|
-      @task = Task.find(params[:id])
-      @task.update(task_update_params)
-      format.html { redirect_to tasks_path }
+    @task = Task.find(params[:id])
+    if @task.update(task_update_params)
+      redirect_to tasks_path
+    else
+      flash[:error] = "Task failed to update!"
+      redirect_to tasks_path
     end
   end
 

app/views/tasks/index.html.erb

@@ -1,4 +1,12 @@
 <div id="task-index">
+  <% if msg = flash[:error] %>
+    <div class="alert alert-danger alert-dismissable">
+      <button type="button" class="close" data-dismiss="alert" aria-hidden="true">
+        &times;
+      </button>
+      <strong><%= msg %></strong>
+    </div>
+  <% end %>
   <ul class="list-group" id="tasks">
     <% @tasks.each do |task| %>
       <% if task.completed_flag %>