sending messages ID to client API

[flohoch]

The clients (android & iOS) save the IDs of read messages, thus it might be a more optimized way to send the ID of the last read message to the OnLaunch server which responds with messages with IDs higher than the last read message ID. In case there are currently active blocking messages with a smaller ID, they have to be sent as well.

Check if this approach is feasible and a good idea in general. Possibly implication might be a problem when it comes to manually change the order of message in the frontend. Or in general, when e.g. the server sorts by start and end dates and messaged IDs get shuffled (i.e. ID 13 comes before 7, if 13 is flagged as read, but 7 is not, the next time 7 would not be loaded)