Route splitting

[dabreegster]

We started a tool in ATIP to split an existing route. The splitting logic has to understand the waypoints property and do something non-trivial. This issue is to track moving the logic here, adding tests, and possibly exposing callbacks to do things like updating names of split segments.

• Scissor icon for split tool
• Unit tests
• Move splitting logic to route-snapper
• Automatically update/set the name for split segments. And/or group the split segments together.