Add Settings api, and xpathCompression setting for Android

Same as last, time, you need to use my fork of wd.js to run the tests...
do the other devs agree the event emitter is worth the complexity cost compared to a bunch of if statements?

```
_.each(settings, function (setting) {
  if (setting.key === "xpathCompression") {
    this.setCompressedLayoutHierarchy(setting.value);
  } else if (setting.key === "setting2") {
    this.setSetting2(setting2.value);
  }
});
```