Rename .fileNotReadable to .message-error

refs #9247

application/views/scripts/about/index.phtml

@@ -16,7 +16,7 @@
 
     echo (
         0 === count($versionInfo)
-            ? '<p class="fileNotReadable">' . $this->translate(
+            ? '<p class="message-error">' . $this->translate(
                 'Can\'t determine Icinga Web 2\'s version'
             )
             : '<p>' . nl2br(implode("\n", $versionInfo), false)

public/css/icinga/layout-structure.less

@@ -331,8 +331,7 @@ html {
   position: absolute;
 }
 
-/* TODO: replace this with .error */
-.fileNotReadable {
+.message-error {
   padding: 0.5em;
   background-color: @colorCritical;
   font-weight: bold;