add admin flash messaging and styles

app/views/shared/_generic_flash.html.erb

@@ -0,0 +1,15 @@
+<% if flash[:error].present? %>
+  <div class="error"><%= flash[:error] %></div>
+<% end %>
+
+<% if flash[:success].present? %>
+  <div class="success"><%= flash[:success] %></div>
+<% end %>
+
+<% if flash[:warning].present? %>
+  <div class="warning"><%= flash[:warning] %></div>
+<% end %>
+
+<% if flash[:notice].present? %>
+  <div class="notice"><%= flash[:notice] %></div>
+<% end %>