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-android/src/org/briarproject/android/AppModule.java

@@ -77,6 +77,7 @@ public class AppModule {
 		return new DatabaseConfig() {
 
 			private volatile SecretKey key = null;
+			private volatile String nickName;
 
 			@Override
 			public boolean databaseExists() {
@@ -95,6 +96,16 @@ public class AppModule {
 				this.key = key;
 			}
 
+			@Override
+			public void setAuthorNick(String nickName) {
+				this.nickName = nickName;
+			}
+
+			@Override
+			public String getAuthorNick() {
+				return nickName;
+			}
+
 			@Override
 			public SecretKey getEncryptionKey() {
 				return key;