Use componentDidCatch in markdown renderer

This would prevent crashes in the app like the one in #744, and would allow us to show a nice error message inviting the user to fill a bug report in git-point, prefilling the issue with the markdown that causes the crash :ok_hand:

I almost got it working with RN 0.54 but it still crashes on Android. Issue tracked at https://github.com/facebook/react-native/issues/18491