Update term_checkboxes.class.php

The term_checkboxes option is not getting custom taxonomy and showing post category even when we set it.
Merge pull request #147 from kwayyinfotech/patch-1

Update term_checkboxes.class.php
Performance of post_select increased
Code cleanup
Update id when adding bundle
Better parameter names
De-activate slider

Will come back later
$this->after_id

So we can update the id when using bundles
Version 2.3.3
No ajax save within bundles
Methods to output data_attributes, css_classes, explanation
Docs for Cuztom_Field
Methods for outputting id and name
New helper methods for attirbutes
Rest of the fields with attribute helpers
$id_name instead of $field_id_name
Small updates for new attribute helpers
Explanation for all fields
Url field (not working yet)
Taxonomy and show, sort, filter column