This PR:
- moves wrapping of appliers (due to Alarms) out of server.go into uber_applier.go
- clearly devides the application logic into: chain of:
a) 'WrapApply' (generic logic across all the methods)
b) dispatcher (translation of Apply into specific method like 'Put')
c) chain of 'wrappers' of the specific methods (like Put).
- when we do recovery (restore from snapshot) we create new instance of appliers.
The purpose is to make sure we control all the depencies of the apply process, i.e.
we can supply e.g. special instance of 'backend' to the application logic.
