Add splash screen

[lachlanjc]

No description provided.

[kusti8]

I feel like we should add a quickstart guide that runs one time instead of a splash screen, since the loading time is very small.

[lachlanjc]

@kusti8 Yeah I’ll make a second issue. This is for the screen that shows up while the app loads (on iOS, it’s the default right now, white with “Blink” in bold black), then we definitely want an explainer on the StartScreen to talk about how the app works.