Enhance device management API.

1. Put a limit on the number of registered devices per account.

2. Support removing devices.

3. Support device names and created dates.

4. Support enumerating devices.

// FREEBIE

src/main/java/org/whispersystems/textsecuregcm/controllers/AccountController.java

@@ -282,6 +282,9 @@ public class AccountController {
     device.setSignalingKey(accountAttributes.getSignalingKey());
     device.setFetchesMessages(accountAttributes.getFetchesMessages());
     device.setRegistrationId(accountAttributes.getRegistrationId());
+    device.setName(accountAttributes.getName());
+    device.setCreated(System.currentTimeMillis());
+    device.setLastSeen(Util.todayInMillis());
 
     Account account = new Account();
     account.setNumber(number);