Add better resolving for adapters/serializers

[igorrKurr]

We need to provide resolving and registering for adapters/serailizers like regular ember app does, but also for offline ones, and maybe add some methods to store, like lookupOfflineAdapter.
This can look like that:

//app/adapters/application.js
var offline = LFAdapter.extend(offlineMixin, {...})
var online = RESTAdapter.extend(onlineMixin, {....})

export {offline, online}

Or add to app/adapters ...-offline adapters or separate offline folder from which we can resolve adpaters for offline.