Regional timeserial for a LiveObject:
- is set to StateObject.regionalTimeserial when object is created
during SYNC sequence
- is set to message's channelSerial property when object is
created via a state operation message
- is updated to message's channelSerial property when an operation is
applied on an object via a state operation message
- is equal to zero-value Timeserial (`@0-0`) when creating a zero-value
object

- state operation messages are buffered while SYNC is in progress
- all buffered operations are discarded when new SYNC starts
- when SYNC ends operations to apply are decided based on the regional
timeserial of the message
- eligible operations are applied via a regular LiveObject operation
application logic

Resolves DTP-955

This refactoring is needed for upcoming tests for buffering of state
operation messages.

…f sync sequence