change NamespaceStrategy signature to createNamespace(Repository)

This change allows us to implement NamespaceStrategies, such as by type (git, hg, svn) or manual defined.
The DefaultNamespaceStrategy accepts now a predefined namespace and only if no namespace was set the username of the currently logged in user is used.

scm-core/src/main/java/sonia/scm/repository/NamespaceStrategy.java

@@ -2,7 +2,18 @@ package sonia.scm.repository;
 
 import sonia.scm.plugin.ExtensionPoint;
 
+/**
+ * Strategy to create a namespace for the new repository. Namespaces are used to order and identify repositories.
+ */
 @ExtensionPoint
 public interface NamespaceStrategy {
-  String getNamespace();
+
+  /**
+   * Create new namespace for the given repository.
+   *
+   * @param repository repository
+   *
+   * @return namespace
+   */
+  String createNamespace(Repository repository);
 }