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>
@mach6 
On a second though, I think adding a file to the monitoring folder should not raise exception since we don't want to stop the running node with something not related to the node. Can we just simplify catch the exception and output an info siting the reason that file could not add to the folder? If there is a problem processing files already exist in this folder before starting the node then we should throw an exception as it used to be for the "-aut" parameter.