Ensure TRRefreshControl ends refreshing on main thread
Ensure TRRefreshControl ends refreshing on main thread

Instead of expecting upstream producers to emit events on the main
thread, it's more robust to have `TRRefreshControl` hop to the main
thread when it knows it needs to update the UI.

faimin/Tropos,thoughtbot/Tropos,faimin/Tropos,thoughtbot/Tropos,faimin/Tropos,thoughtbot/Tropos