create function to allow easy acces to progress bar markup

I had a case where I was using panels to override the node template for a node that had a payment form on it. In order to show the progress bar within a panels pane - I had to:

1) do a separate call to node_load even though the node object is already loaded once
2) manually call pay_node_nodeapi with the $op = 'view' to get it to add the 'pay_node' content to the node
3) call drupal_render to get the pay_node content rendered as HTML.

pay_node should provide a simple function that would let me retrieve the markup for a payment progress bar without having to jump through all those hoops. - And it would be super cool if I could create a progress bar regardless of how the default payment form rendering is set for the given node.

The attached patch creates a function pay_node_progress_bar($node,$paid,$html) that makes it simple to grab a progress bar for either total paid ($paid = TRUE which is the default) or total amount ($paid = FALSE). Output is returned either as formatted HTML ($html = TRUE - defualt) or as an FAPI array