Make Rendering classes usable from a non-component environment

If we want to separate the Rendering from XWiki Core so that it becomes a top level project and is usable standalone without requiring to have XWiki installed then we need to make it usable without requiring Plexus and without requiring private member field injection. For this we need to do 2 things:

• Add setters to set the private fields
• Make the implementation classes user public, ie move them out of the internal package

As an example we'd need to be able to register a transformation against the transformation manager, and to be able to register macros against the macro transformation. Something like this:

MacroTransformation macroTransformation = new DefaultMacroTransformation();
macroTransformation.registerMacro(new GroovyMacro());
TransformationManager manager = new DefaultTransformationManager();
manager.registerTransformation(macroTransformation);

Note that we might need to add some non default constructors too and to move things around a bit.