Add OpenAndHide action

This is an action that I am missing quite a bit in ControlPlane -- to not just open a given application (or a file), but also to launch it hidden. Much like what I can do with "Login Items" in OS X 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 simple and useful action shall be among the basic ones.

Please, review and let me know if the changes proposed look good to you. I have tested this code on my MBP during the day today. Works really well for me -- both for the existing ("simple") Open action and for the new OpenAndHide action.

I hope that other users will also like this small addition.