Possibility to show track of an older hike along with current track

[AlainKnaff]

📝 Possibility to show track of an older hike along with current track

📖 Description

This adds the possibly to overlay an older track over the current track. Older track will be shown in red (versus dark blue for the current). Accessible from the map display activity using the "hamburger" (3 dots) menu at top right, and choosing "Overlay other".

This is useful when walking near a place where you've been before, in order to compare.

✅ Pull Request Checklist

• The PR is proposed to the DEVELOP branch.
• The changes have been tested on the target Android API and minimum Android API.
• Automated tests have been added (if applicable).
• The feature is well documented.
• There is a reference to the original ISSUE and related work.

[AlainKnaff]

I've rebased on the latest develop to account for recent schema changes.
Also cleaned up lots of messy test commits.

Ready for review whenever.

Thanks