Simplify UI by combining dualistic POI and GPX selection screens

[sonora]

For both POI, and GPX tracks, we currently offer 2 different selection screens (and ways to select and display) these objects on the map. They have different look and feel, and slightly different capabilities, and users are often aware of only one of them. This leads to

• users finding one of the ways but not discovering the other one, hence "missing" essential e.g. search or filter functionality
• a significant number of support cases
• also more code we have to maintain

POIs or GPX tracks can be placed on the map either via the "Configure map" button and a flat list selection screen, or via the dashboard's "Search -> Show all" screens, which have more functionality like text filtering, items structured by folders, etc..

I suggest that we abandon the "flat list" selection screens, instead tapping on the "POI..." or "GPX Track..." menu entries in the "Configure map" menu must lead to the exact same (full functionality) screen we already have for "Search -> Show all". Future development can then concentrate on only these full functionality selection screens (like when we e.g. implement a "Sort by date" view of the GPX tracks or similar. And users have to handle fewer different screens, which simplifies the app and makes it more likeable :-)

[vshcherb]

Requires a little bit more thinking.

[dbrgn]

@sonora commented in #9857

Side note: The much more powerful way and screen to access track-related functionality is really via Menu/MyPlaces/Tracks. Many users do not know hence #1435.

That is correct, I was not aware of that page. It would be great if this could be made a bit more prominent. I also would not have expected tracks to be under a category called "Places". Maybe "Places / Tracks"?