Add Rainmeter.exe.config to declare support for the .NET 4.0 and 4.5 runtimes
This allows plugins like InputText.dll to be used with .NET 4.0/4.5 in addition to 2.0. Therefore, we can avoid installing .NET 2.0 on Windows 8 and 8.1 where it is not installed by default (whereas 4.5/4.5.1 is installed by default).