Implement a better data structure to store policies

Implement a better data structure to store policies

A new map-based structure was used to store policies
in Cynara::PolicyBucket. This allows policy checks
to be much faster.

PolicyBucket interface was changed, so the operation
required a lot of refactorings across many storage classes.
Most of functions are now simpler, clearer and decoupled
from each other. Tests has been adjusted. No public API changes
were required.

Change-Id: Ida9dc8eb31120b27cf9547e56840dd27390de247