Add applet initialization callback

A mechanism of callback function has been implemented in the JApplet. But it is not an anonymous callback function, because the JApplet calls a Javascript method by its name, and thus it needs to know its name. Moreover, as the Java JSObject call method does not allow to call a namespaced function, a binding between the name of the callback function (without namespace) and its real name (with namespace) must be add at the end of the Javascript file (websampconnector.js). By default, the callback function is the setStatusIcon method.