Linking multi activity trips

The most likely item would be someone doing bike packing where they go from road to trail.  Or there's a few areas with float + backpacking trips where you walk back to the start. 

It would be useful to be able to switch the type mid-recording and it changes the color on the resulting map and you get data for both types.  Overall distance and speed and then specific mode information.  

Instead of necessarily changing the type mid-recording, be able to make two activities and link them into one trip and they appear on one map