Changed Blink1Lib assembly to use .NET 4.0

It will most likely not use any of the new v4.5 features.
Added wrapper for openBySerialNumber method
Added wrapper for getVersion method
Cleanup using statements and removed Main method

The Main method is not used
Change null check to "!= IntPtr.Zero"

More cleanup as well and naming of _connectedDevice pointer.
Made DllImports private to not expose internal stuff
Updated Blink1.cs to follow .NET coding standard