Make a private method visible to subclasses

So that users can change the model used to render templates if they
have custom requirements for additional content.

initializr/src/main/groovy/io/spring/initializr/ProjectGenerator.groovy

@@ -162,7 +162,7 @@ class ProjectGenerator {
 		}
 	}
 
-	private Map initializeModel(ProjectRequest request) {
+	protected Map initializeModel(ProjectRequest request) {
 		Assert.notNull request.bootVersion, 'boot version must not be null'
 		def model = [:]
 		request.resolve(metadata)