fix: do not reset the distance in the distance comparator

The distance comparator should not override a distance that can have
been obtained from the website and that we are unable to recompute
locally (because we don't know the cache coordinates for example).

Part of work on #2733.
fix #2733: acquire distance and direction for basic members

A recent change in geocaching.com way of presenting the distance and
direction information for basic members requires a new parsing.
refactoring: share the name of the shared image directory

Part of work on #2733.
enhancement: share direction images for basic members

Use the regular images cache for basic members direction images in cache
list.

Part of work on #2733.
enhancement: make the distance comparator work with approximate distance

Part of work on #2733.
fix: parse basic member difficulty and terrain

Part of work on #2733.
fix: parse basic member size

Part of work on #2733.
Merge branch 'fix-2733' into release