improve the GPX example tracks

[Martin Kolman]

• name all example tracks example_something to differentiate them from user created tracks
• sort out the current tracks
• add at least one real log
• add some tracks representing various regions from openrouteservice or other OSM based routing provider
  • Brno - Vienna
  • something in America & Japan
  • Kremlin to Gum in Moscow ? :)
  • other ?
• keep the combined size reasonably small