Initialize cursors backing MessageCollections
Timestamp values in ms, not s
Edge case handling in BLETransport

Avoid NPE when no identity available for device, no messages available
for sending.
Fix used wrong RequestType enum in BLEPeripheral

Used BLECentralRequest.RequestType in BLEPeripheral caused responses to
not be matched to requests.
ChatApp fixes.

Register TransportCallback, fix iterating beyond bounds of returned
messages in getMessagesForIdentity
BLECentralRequests may abort request per Peripheral

Also fix issues with central -> peripheral request flow.