Removing network manager / refactoring metadata manager to use RestRequest and RestClient

Also new rest wrappers for search scope and order / search result layout
Tests for new wrappers
This is a one-off case for the ```PushService```. I don't know if we should expose this approach to getting a ```RestClient``` for other components. The other components should probably directly use ```ClientManager``` to get ```RestClient```.

I'd prefer this stayed in ```PushService```, and we use ```clientManager.peekRestClient(userAccount)``` directly in ```MetadataManager```.