added a cache to the IdentityManager, changed its signature, modified when and where the author is stored

made the author creation single-threaded again in the LifecycleManager, removed redundant code

briar-tests/src/org/briarproject/TestLifecycleModule.java

@@ -38,7 +38,7 @@ public class TestLifecycleModule {
 			}
 
 			@Override
-			public StartResult startServices() {
+			public StartResult startServices(String authorNick) {
 				return StartResult.SUCCESS;
 			}