Add template part option to post display elements in Theme Blvd Layout Builder. -- Later, we can add to this a way to actually apply the option by creatively filtering themeblvd_template_part or with new filter proposed #224 in Jump Start repo.

functions.php

<?php
/**
 * Add template part option to post display
 * elements.
 */
function my_elements( $elements ) {

	$option = array(
		'id' 	=> 'part',
        'name'	=> __('Template Part (Optional)'),
        'desc'	=> __('Enter in a custom template part for this element. For example, entering "foo" will pull content-foo.php from your child theme for each post in the loop.'),
        'type'	=> 'text'
	);

	$elements['blog']['options']['part'] = $option;
	$elements['post_grid']['options']['part'] = $option;
	$elements['post_list']['options']['part'] = $option;
	$elements['post_showcase']['options']['part'] = $option;

	return $elements;

}
add_filter( 'themeblvd_elements', 'my_elements' );

// @TODO ... Now, how to implement option? Possibly through 
// new propsed themeblvd_{$element_type}_options filter, 
// Jump Start issue #224.