editable description

[``* `#16988` editable description``](http://community.openproject.org/work_packages/16988)
In the last comment (that for whatever reason disappeared) I actually mean the whole object so this becomes:
```JS
var PREVIEW_BUTTON_ATTRIBUTES = {
  "class": 'btn-preview',
  type: 'button',
  text: I18n.t('js.inplace.button_preview')
};
var previewButtonAttributes = PREVIEW_BUTTON_ATTRIBUTES;

previewButtonAttributes.click = function() { ... };

element.closest(".ined-input-wrapper")
       .find(".help")
       .before(jQuery("<button>", previewButtonAttributes));
```