Ability to combine routes

🚧 THIS IS A TICKET MIGRATED FROM UPVOTY. The original ticket and comments will be available for a limited time over at:
https://abrp.upvoty.com/b/request-a-feature/ability-to-combine-routes/
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I would like to see the ability to combine two (or more) saved routes into a new plan. When going on long extended road trips (several weeks), it's nice to break up planning into smaller segments to reduce the total number of stops in a single plan. It would be great to have the ability to merge multiple plans into a single large plan when done (or to combine different potential routes into a complete plan).