Migrate network configuration into NetworkController

[Gudahtt]

The network configuration is currently stored in the PreferencesController. We should migrate it to the NetworkController instead. The network controller is a more sensible place for managing network config, and this will make multi-network support easier to manage (it needs to know which networks exist in config to manage active network connections).

[mcmire]

Rough plan:

• (controllers) Keep a list of networks
  • Each network should have its own id, which we can expose to the UI for updating/deleting networks or switching networks
  • Add new CRUD methods in NetworkController for the list (keep existing methods as they are)
  • Add new way to keep track of which network is current (and add method to get it)
• (controllers) Prepare for removing address book syncing code from PreferencesController
  • Add onNetworkStateChange to AddressBookController
  • Copy code in PreferencesController around updating address book (indirectly) to AddressBookController
• (extension) Wire up new changes
  • Update controller instantiation code in MetamaskController to pass onNetworkStateChange to AddressBookController
  • Change actions bound to the UI to use NetworkController methods instead of PreferencesController methods (includes bound methods in MetamaskController)
  • Update NetworksTab component and Redux selector to pull network list out of state correctly
  • Remove network code from PreferencesController and related actions
  • Update existing NetworkController methods to use new methods (and add logic when switching networks to validate that the passed in provider config matches a network in the list)
• (mobile) Wire up new changes
  • Update controller instantiation code in Engine to pass onNetworkStateChange to AddressBookController
  • Change UI code...