Add cancel button to editor. Resolves issue #1282.

lib/gollum/public/gollum/stylesheets/editor.scss

@@ -318,13 +318,14 @@ a {
 
   /* @control preview */
 
-  #gollum-editor-preview {
+  #gollum-editor-preview, #gollum-editor-cancel {
     float: left;
     font-weight: normal;
     padding: left;
 
     @include alt-box-model;
   }
+    
 }
 
 /* @control title */

lib/gollum/templates/editor.mustache

@@ -146,6 +146,7 @@
 
     <span class="jaws"><br></span>
     <input type="submit" id="gollum-editor-submit" value="Save" title="Save current changes">
+    <a href="" id="gollum-editor-cancel" class="minibutton" title="Cancel editing" onClick="window.history.back()">Cancel</a>
     <a href="{{base_url}}/preview" id="gollum-editor-preview" class="minibutton" title="Preview this Page">Preview</a>
   </fieldset>
 </form>