Add TODO for not allowing double account creation

bramble-core/src/main/java/org/briarproject/bramble/account/AccountManagerImpl.java

@@ -159,6 +159,7 @@ class AccountManagerImpl implements AccountManager {
 	@Override
 	public boolean createAccount(String name, String password) {
 		synchronized (stateChangeLock) {
+			// TODO don't allow creating another account if one already exists
 			LocalAuthor localAuthor = identityManager.createLocalAuthor(name);
 			identityManager.registerLocalAuthor(localAuthor);
 			SecretKey key = crypto.generateSecretKey();