Ability to Order files in wpdm_tree [WPDM Extended Shortcodes]

Included is the updated file, with a git-diff of the original plugin file and the updated file.

This update allows the wpdm_tree shortcode to accept order_by and order parameters, in accordance with the capabilities of WP_QUERY()

[wpdm-extended-shortcodes.php]
It first accepts the parameters and assigns the current default values (order_by = ID, order = DESC) if not defined. (~ line 21)
Sends these parameters in the AJAX request. (~line 30)
Accepts the AJAX parameters (~line 410) and applies them to the WP_QUERY() params (~line 420)

Example:
[wpdm_tree category="policy-documents" download_link="1" order_by="title" order="ASC" ]

Thanks again and I hope this helps!

Test Cases:

// No values
[wpdm_tree category=”agency-policy” download_link=”1″]

// Valid values
[wpdm_tree category=”agency-policy” download_link=”1″ order_by=”title” order=”ASC” ]

// Invalid Values
[wpdm_tree category=”agency-policy” download_link=”1″ order_by=”SOMETHING_IMPOSSIBLE” order=”NOT_ASC_OR_DESC” ]

Also, $order should probably be strtoupper($order) as WP_QUERY only accepts upper case for that option.