Deployment Guide, enhance Example 5-1, Creating a dtjava.App Object

From Igor:

// Undocumented, but first param is URL, 2nd is a set of properties that must include width, height, and placeholder for embed().
var app = new dtjava.App(
'ssh.jnlp',
{
    id: 'SSH',
    width: 100,
    height: 25,
    placeholder: 'SSH_applet_container',
    params:
    {
        config: 'ssh_applet.conf',
    }
});

We do not say placeholder is required. We do say it about width and height.
May be we need to highlight requirements more?

And perhaps make sense to add signature for App/Platform like we do later for callbacks.

E.g.
   dtjava.App(url, {attibute_map});