Offline: Remove downloaded area and view details

[yo1995]

Description

This PR adds 2 features

• Remove downloaded files for a preplanned map area
  • By swiping the list row to the left, a delete button is revealed. Once tapped, the directory of the preplanned map area is removed from local disk
  • If an area is currently open but is removed, the selectedMap binding will be set to nil so the online web map is used instead
• View the metadata of a preplanned map area
  • Tapping on the list row will reveal the metadata view, similar to App Store listing
  • Currently it get all the metadata from the downloaded files. In the next on-demand workflow, some metadata will be serialized when the area is downloaded

[des12437]

Looks good. There is a bug where selectedMap is set to nil every time a map area is deleted, but that should be fixed in the PR to improve selection logics right?

[yo1995]

Thanks for approving! I was hoping #867 can get reviewed first and merged into this branch. Then I'll merge this PR.