Unified Storage Architecture

Introduced new types store sbiStore pndStore and deviceStore. Based on map[uuid.UUID]Storable the store type is meant to be a wrapper around maps, able to store anything that satisfies the interface Storable. It is defined as folows

type Storable interface {
	Id() uuid.UUID
}

Having the store-family I'd like to deprecate any direct access to maps. Feedback and review appreciated.