Easier customization of SchemaFactoryWrapper

Hello,

It seems that SchemaFactoryWrapper was designed to allow customization. This patch makes it easier to customize the SchemaFactoryWrapper:
 * the JsonSchemaGenerator constructors may now take a WrapperFactory as an argument, so that it can be used with subclasses of SchemaFactoryWrapper
 * the FormatVisitorFactory now allows to define the WrapperFactory that will be assigned to visitors of structured schemas (object, array, map)
 * consequently, the constructors of visitors of structured schemas (ObjectSchemaVisitor, ArraySchemaVisitor, MapSchemaVisitor) may now take a WrapperFactory as an argument.

I tried to keep changes to a minimum. This patch does not break the API and should not change the operation of current code based on the API. In fact, it merely adds new constructors.

Note : I also fixed a typo in a test (TitleSchemaFactoryWrapperTest.java). I noticed it while tweaking this patch.