Added folder monitoring capability and fixed emulator launching problem.

- The folder monitoring allows users to add one or more native android
apps on fly and selendroid immediately signs and adds these files to
the app store so they can be used without restarting the node.
- Adding one seconds wait before calling "isDeviceReady" to avoid the
command sent too quickly while the emulator still starting and not ready
to receive any commands

Signed-off-by: Binh Vu <bvu@paypal.com>
Before this change the exception was propagated, leading to a catch an log message in the [`SelendroidLauncher`](https://github.com/selendroid/selendroid/blob/master/selendroid-standalone/src/main/java/io/selendroid/SelendroidLauncher.java#L63-L68). Not sure if things will break or get less clear now you're catching it here.