Add livetable configuration to specify that an action should be executed asynchronously

Livetable actions are regularly URLs that the browser ends up following and the user will leave the livetable page to follow the action that he wants to execute.

However, some actions are instance (i.e. require no user interaction), so there really should be no need to leave the current page and the action could be handled asynchronously (with AJAX).

Another thing to consider would be to also report the status of the action (success/fail/question).

Coupled with XWIKI-14350, it would make the livetable's actions more usable and would minimise page reloads.