Refactor client API

[dmaretskyi]

From client class move all of the fields required solely for devtools into a separate sub object DevtoolsContext:

• Define DevtoolsContext interface
• Should have at least
  • reference back to Client
  • feed store
  • network manager
  • model factory
• Context should have a reference back to the client
• Add a method to client getDevtoolsContext()
• In client provider make sure to assign window.__DXOS__ to this new context
• Fix any usages in devtools