Add OpenAndHide action

This is an action that I am missing quite a bit in ControlPlane -- not only to open an application (or a file), but also to launch it hidden. Much like what I can do with "Login Items" where I can set the "Hide" flag for an individual application.

Though that functionality can be achieved in ControlPlane with the existing actions plus scripting, I strongly believe that such a basic and useful actions shall be among the basic ones.

Please, review and let me know if the changes proposed look good to you. I have done quite a bit of testing with this code on my MBP during today. Works well for me.

I hope other users will also like this small addition.