Private constructors

Many of the `SomethingUtils` classes are able to be default-constructed.  Do we really need an instance of `GeometryUtils` floating around people's code?

This PR does not `static`-ify existing classes (e.g. classes like `ConvexHull` and `Sort` are left as is).  This just removes the default constructor for any class with no instance methods or instance fields.  Such classes are as follows:

- `Utf8`
- `BufferUtils`
- `NumberUtils`
- `TimeUtils`
- `ThreadUtils`
- `ArrayReflection`
- `ClassReflection`
- `Numbers`
- `Box2DBuild`
- `Controllers`
- `FireTV`
- `Ouya`
- `FreetypeBuild`
- `Gdx`
- `Version`
- `PixmapIO`
- `ETC1`
- `GeometryUtils`
- `Intersector`
- `MathUtils`
- `HttpParametersUtils`
- `Actions`
- `Align`
- `UIUtils`
- `GdxBuild`
- `GdxNativesLoader`
- `ScreenUtils`
- `StreamUtils`
- `Lzma`
- `Base`