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>
The old logic would check if the app didn't already exist in the store. Should it still be an option to check that instead of always just adding it?