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 @binhvu 

Wouldn't it be a bit more simpler to bring in the folder monitoring capabilities if and only if the `-folder` parameter has been specified ?

That way the user gets the normal behavior if this argument is missing and gets the monitoring behavior if this argument is present. We also get to save on an adding an extra argument just for the enabling/disabling sake.