Numerous updates to observation flow

* Added back button to camera
* Added prev/next buttons to Media Viewer
* Camera flow skips group photos when there's only one photo
* Added support for custom fonts (currently Whitney)
* Sync button in toolbar on My Obs turns green when obs to sync
* ObsEdit fetches location until good enough for new obs
* Bottom sheet hides when you scroll My Observations
* Toolbar on My Observations sticks on scroll
