Warn users when their keys are invalid

app/helpers/form_helper.rb

 module FormHelper
-  def form_errors(model)
+  def form_errors(model, headline = 'The form contains the following')
     return unless model.errors.any?
 
     pluralized = 'error'.pluralize(model.errors.count)
-    headline   = "The form contains the following #{pluralized}:"
+
+    headline = headline + ' ' + pluralized + ':'
 
     content_tag(:div, class: 'alert alert-danger', id: 'error_explanation') do
       content_tag(:h4, headline) <<

app/views/profiles/keys/_key.html.haml

 %li.key-list-item
   .pull-left.append-right-10
-    = icon 'key', class: "settings-list-icon hidden-xs"
+    - if key.valid?
+      = icon 'key', class: 'settings-list-icon hidden-xs'
+    - else
+      = icon 'exclamation-triangle', class: 'settings-list-icon hidden-xs',
+        title: 'The key is disabled because it is invalid'
+
+
   .key-list-item-info
     = link_to path_to_key(key, is_admin), class: "title" do
       = key.title

app/views/profiles/keys/_key_details.html.haml

@@ -16,6 +16,7 @@
           %strong= @key.last_used_at.try(:to_s, :medium) || 'N/A'
 
   .col-md-8
+    = form_errors(@key, 'The key has the following') unless @key.valid?
     %p
       %span.light Fingerprint:
       %code.key-fingerprint= @key.fingerprint