Install Image Gallery plugin to CKEditor

Unpack archived files directly to ckeditor/plugins.
Turn on the plugin in ckeditor/config.js:
```
config.extraPlugins = 'jsplusGallery';
```
Add these buttons to the toolbar definition:
- jsplusUploadGallery
  Insert a gallery
See sample CKEditor toolbar configuration to find out more about this step.
Now you can use your installed plugins. Do not forget to sure that browser cache was cleared.