Use a copy of user identifier on alias method

Signed-off-by: Miguel M. Almeida <miguelcma@gmail.com>
Serialize DP to json outside of queue + atomic

on DP main entities (User, Device, Session, Device, DataPoint).

This solves a lot of concurrency problems and reduces consumption of memory.

Signed-off-by: Miguel M. Almeida <miguelcma@gmail.com>
Fix tests that now use a single Liquid instance

instead of Liquid singleton.

Signed-off-by: Miguel M. Almeida <miguelcma@gmail.com>
[Release] New Liquid iOS SDK release: v0.9.3-beta

Signed-off-by: Miguel M. Almeida <miguelcma@gmail.com>