Add state to TKServer

The state is a global state of the user that can be used to determine exactly what the app should show when activated
Update `state` in every response

Every server response now returns a "state". If it does, `TKServer` now updates the `state` variable so app can observe it and change UI accordingly.
Start bluetooth as soon as we have a user ID

As oppose to starting it only when the user accepts their target. We want the device to be discoverable as soon as possible, so that as soon as the game starts, killing can begin.
[UNFINISHED] Refactor UI state management

Basically, the new design is as follows:

 1. Server returns 'state' field in every response.
 2. TKServer updates their `state` global variable
 3. `TKAppViewController` observes `TKServer.state`
 4. Whenever the state _changes_, `TKAppViewController` folds back the navigation 
    stack and pushes on the view controller scene based on the new state.

This actually moves control of state management to one place: the server.
Cocoapods!
add won and lost states
Show alert view when killing failed
Clean all warnings
Prefetch profile photos