New photo picker

[stuartpb]

Rather than using Filepicker, it'd be better to just have a more straightforward file selector (hooking directly into the OS's Camera/Gallery dialog) that immediately shows the photo full-screen after selecting (like Foursquare/Swarm does).

We can also prompt the user then to "tap the plug" to confirm. This avoids badly-centered photos, provides a seamless confirm/back mechanism (with silent implicit enforcement of good centering), and mandates a really important part of the UI (which can be played with in presentation).