Support editable trees, which is needed if we want a usable checkbox column in a...

Support editable trees, which is needed if we want a usable checkbox column in a tree.
And, support checkbox columns in trees.

An example:

<tree id="my_list" editable="true" />

JSAN.use('util.list');
var list = new util.list('my_list');
list.init( {
	'columns' : [
		{
			'id' : 'select',
			'type' : 'checkbox',
			'editable' : true,
			'label' : '',
			'render' : function(my) { return true; } // Checked by default
                }
	]
} );

But once a tree is editable, all tree cells are editable unless explicitly made otherwise, so you need 'editable' : false in the column definitions for such trees if you don't want cells in those columns to be editable.

git-svn-id: svn://svn.open-ils.org/ILS/trunk@14391 dcc99617-32d9-48b4-a31d-7c20da2025e4