Add quickselect algorithm. Quickselect is a selection algorithm to find the kth smallest element in an unordered list.

1. go to https://graphhopper.com/maps/
2. from/to text fields are empty, click one of the vehicle icons
3. right click the map -> 'Set as Start/Intermediate/End' entries are grayed out
4. (bonus) click vehicle icon again -> markers are created in Sibay, Russia, context menu entries become active again, but from/to fields still empty even though there are markers on the map

I ran into build problem with tests. We may be missing a dependency check for spatialite-tools on a fresh build, but don't explicitly check for its existence when building the test target. As a result, the test target fails downstream when a require data dependency is missing.

Here's the error I got:

$ mkdir build
$ cmake