scorm_get_toc rewrite

scorm_get_toc needs a rewrite as it doesn't always generate valid html for complex scorm packages and doesn't contain the information in a easy to parse manner for other functions (like seq/nav for SCORM 2004)

We need at least 3 new functions.
scorm_get_toc_object()
this should be based on the existing scorm_get_toc but instead of generating html, it should generate an object that can be parsed to create the html - this function should take the data from a call to scorm_get_scoes and return each sco in a formatted object with these extra params:

$sco->url = ''; //this isn't a full url, just the bits required to link to the sco - this is what is inserted into the 'title' tag in the yui treeview.
$sco->statusicon = '<img>'; //this is the status icon that should be displayed with the sco
$sco->children = array() - this contains an array of any children $scos formatted in a similar way.

Then a separate function
scorm_format_toc_for_treeview()
which takes the output of scorm_get_toc_object() and generates the html used by the YUI treeview object.

Then a separate function
scorm_format_toc_for_droplist()
which generates a drop list used by $result->tocmenu for the drop list nav item.

Finally another function scorm_get_toc_new() - this function should return the exact same information as the existing scorm_get_toc() but using the new functions above so we can easily swap between using the old scorm_get_toc() and the new scorm_get_toc_new()

these functions should all be in mod/scorm/locallib.php and the changes shouldn't modify any existing functions. It is preferred if the existing functions don't do what is required then we duplicate that existing function under a new name and change the "new" copy of that function. Doing this means we can compare the existing scorm_get_toc with the new code to make sure the new one operates as expected.