Move IComponentFactory from EntryPoints namespace

[eerhardt]

The current IComponentFactory types are in the Microsoft.ML.Runtime.EntryPoints namespace.

machinelearning/src/Microsoft.ML.Core/EntryPoints/ComponentFactory.cs

Lines 7 to 12 in 841ba78

	namespace Microsoft.ML.Runtime.EntryPoints
	{
	/// <summary>
	/// This is a token interface that all component factories must implement.
	/// </summary>
	public interface IComponentFactory

We should move them to a more appropriate namespace, since EntryPoint doesn't really make sense, they are used outside of EntryPoints. I think they should go in the same namespace as the ComponentCatalog.

Also, we should remove the IArgsComponent interface, as I don't see it serving any purpose.

/cc @TomFinley @Zruty0 @codemzs