ReduksBus API overhaul

New features
Reduks bus api vastly improved: see the sources and updated Readme
Breaking changes
in ReduksBus api:

• unsubscribeAllBusDataHandlers renamed to removeAllBusDataHandlers

in Reduks interface

• removed storeSubscriber and storeSubscription fields
• added instead maps storeSubscriptionsByTag and busStoreSubscriptionsByTag that can be accessed by tag
• added 'reduks' interface extensions methods for more easily managing store subscriptions: subscribe that automatically
  store subscription with tag, and unsubscribe that retrieve a subscription by tag and unsubscribe it

Dependencies updated

• kotlin : 1.0.6
• android support lib: 25.1.0