[Fixes #9] Increase multidevice response

[cammellos]

We only generate the bundle once every 6 hours (or if pairing information changes). This means that in some cases where many devices appear/disappear, new devices are not picked up until the bundle is refreshed.

For example:

Alice creates a device with timestamp t1 A1 Alice creates a device with timestamp t2 A2 Alice creates a device with timestamp t3 A3 Alice creates a device with timestamp t4 A4

Alice propagates this to bob, bob's list of active devices for alice is now: t2 A2, t3 A3, t4 A4 as we only keep maximum 3.

If Alice sends a message to Bob from A1, previously it would be still using t1 (as long as less than 6 hours have passed).

Now instead the new bundle will have t5 instead, so upon receiving the message bob will have: t3 A3, t4 A4, t5 A1.

This commit changes the behavior to always update the timestamp before publishing the bundle, so that as soon as a message is received from a new device, it will increase the timestamp for that device.

Please don't merge until successfully tested.

Testing

1) Create device B1 2) Create device A1, enabled device-to-device, send a message to B 2) Create device A2, enabled device-to-device, send a message to B 3) Create device A3, enabled device-to-device, send a message to B 4) Create device A4, enabled device-to-device, send a message to B 5) Send a message from B1 to A 6) A2, A3, A4 should receive the message 7) Send a message from A1 to B 8) Send a message from B1 to A

In develop A2, A3, A4 should receive the message In this pr A1, A3, A4 should receive the message

[cammellos]

@adambabik added comments, let me know if it's ok!