* Extracted non-photo stuff from PhotoDisplay
* Separate component for FaveButton
* Prevent faves while signed out
* Separate component for nav header
* Stick nav header while scrolling until tabs
* Nav header has slight gradient for visibility over white content
* Renamed ObsDetails media components so they're not focused on photos
* Data and layout changes leading up to sound player on ObsDetail
* Add sound player to ObsDetails
* Swiping away while playing should pause playback
* Swiping back to sound and playing again should resume where you left off
* Allow viewing media while offline (images may be cached)
* Stop playback when navigating away from ObsDetails
* Fetch sounds in Explore so we can show sound icon
* Map all observation objects in explore with Realm-ish attributes
