add disable shortcode attr and filter, add submit id
add disable shortcode attr and filter, add submit id

- add a possibility to disable submit button by default via shortcode attribute e.g. when we want to enable it via java script `[paylane_plugin disabled=disabled]`
- add a filter to disable/enable submit button via functions.php or custom plugin
- add css class `wp_paylane_pay_button` to easy get input in javascript
PayLane/plugin_wordpress_donate