Removed react-native-router-flux and added custom navigation logic

[hmhealey]

The basic way this works now is that we have the navigation section of the redux store that's controlled with standard actions and a reducer. Right now, it only uses simple actions that push, pop, and reset the stack, but it has support for anything that NavigationExperimental can handle.

Since this is based off the store changes, here are the changes specific to this PR: b1d9c63...e4f7a63

Overview of directory changes:

• src/actions/navigation - For simple navigation actions that can be reused. It might make sense to move these into view actions in the future since while they seem reusable now, they'll become more view specific once we tighten up the app navigation fow
• src/navigation
  • .../router.js - This is what uses the navigation state to render the whole app using NavigationExperimental. It also renders things like the navigation bar and transitions.
  • .../routes.js - These are plain objects representing each route in the app. It can also store properties of that route such as whether it has a title, back button, how it transitions, etc
    -src/scenes - This used to be named src/routes, but I think it was a good idea to separate the definition of a route (which usually involves how you get there) from a scene (which is the actual contents of the route) and to make it more clear that this navigation isn't using a router with a path like we had before.
  • .../index.js - This provides a function mapping route keys to the scene that they use. This could've just been a field in src/navigation/routes.js, but I wanted to keep them separate to simplify dependencies because the actions and reducer for navigation both import routes.js

[enahum]

OK lets merge my PR first so this one get a lot smaller (I think) and after that I'll review