add 'jars` and `midletClassName` URL params

This change adds a URL query parameter parser and support for two params:

* `jars`: a colon-delimited list of JARs to load (in addition to classes.jar and tests.jar);
* `midletClassName`: the name of a MIDlet class to launch (default: *HelloCommandMIDlet*).

With this change, you can start a MIDlet in j2me.js with a URL like:

    http://localhost/path/to/j2me.js/?jars=MyMIDlet.jar&midletClassName=com.example.mymidlet