Attempt at fixing  #2052

This is my attempt to adding an offset parameter to pods shortcode. I added offset to $defaults, with a default value of null and added the offset value to $params passed to pods::find() if offset !is_null. Offset has no effect in the shortcode in my tests.

I tested with this shortcode `[pods name="cpt" offset="5" ]{@post_title}<br>[/pods]` It returned all 7 posts in the CPT called cpt.

I also did this as a test:
`<?php
$params = array( 'offset' => 5);
$pods = pods('cpt', $params );
echo $pods->total();
?>`
And the result was 2, which was  expected (7-5=2).