Remove jQuery usage

Problem/Motivation

Currently, this module uses jQuery directly to work with the HTML. Nowadays, there is a trend to stop using jQuery as:

• Latest JS versions provides the functionality provided by jQuery.
• jQuery has a performance impact in browsers

Proposed resolution

Adapt ajax_blocks.js to use javascript native functions / drupal core JS libraries (s.e.: drupal.ajax, once).

After doing all this, the only remaining piece of code using jQuery will be drupal.ajax, that is a indirect dependency. As soon as Drupal core stops using jQuery in its drupal.ajax library, the module won't be dependant on jQuery anymore.