Add support for URI's path prefix modification

[big-cir]

Overview

1. Added pathPrefix field and setter method to UriModifyingOperationPreprocessor
2. Added corresponding support in UriModifyingContentModifier

Related Issues

#945

Test

@Test
public void requestContentUriPathIsPreservedAndAddPathPrefix() {
    this.preprocessor
		    .removePort()
		    .pathPrefix("/addPathPrefix");
    OperationRequest processed = this.preprocessor
	    .preprocess(createRequestWithContent("The uri 'http://localhost:12345/foo/bar' should be used"));
    assertThat(new String(processed.getContent())).isEqualTo("The uri 'http://localhost/addPathPrefix/foo/bar' should be used");
}

@Test
public void responseContentUriPathIsPreservedAndAddPathPrefix() {
    this.preprocessor
		    .removePort()
		    .pathPrefix("addPathPrefix");
    OperationResponse processed = this.preprocessor
	    .preprocess(createResponseWithContent("The uri 'http://localhost:12345/foo/bar' should be used"));
    assertThat(new String(processed.getContent())).isEqualTo("The uri 'http://localhost/addPathPrefix/foo/bar' should be used");
}