Opt-out option in dialog

Adds a new radio button to the first-time popup that also asks the user if he wants to enable the statistics collection. I also moved a couple of checks in the start method so that the popup is executed first.

If I understand how the unity GUI stuff works, it *should* start enabled (it does in my install).

You will also want to edit the text in the popup I guess.
These HintPaths would make the solution unbuildable by anyone without the same folder structure to find the references in.

I'd recommend putting a `Dependencies` folder at the solution root and referencing the assemblies from there, that way a relative path would be used for the HintPath and people can just be told to place the appropriate assemblies there.

An even better solution would be to include `JsonFx.dll` in the source tree as its [license](https://github.com/jsonfx/jsonfx/blob/master/LICENSE.txt) (MIT) allows, probably with its own license next to it to make it clear Majiir's ARR license does not apply to it. `UnityEngine.dll` may also be included which is allowed [here](http://forum.unity3d.com/threads/unityengine-dll.17569/#post-120067). Unfortunately KSP's own `Assembly-CSharp.dll` would not be redistributable and have to be likely placed in a `.gitignore` so no one commits it.