User location handling

[koebi]

From my POV, there's three main issues with the current user location handling:

1. Currently, the map repeatedly centers onto the user location when "Continuously" is selected.
   This is rather distracting and should be avoided - a first "centering" might be acceptable, but a deliberate "zoom to my location"-button would be more fitting (and also more in line with the crosshair-design of the icon).

2. The "only once"-functionality should still have a "focus on my location"-button. Currently, when moving the map after using the "Only once"-functionality, the location button changes back to the "Show my location"-functionality

3. The crosshairs design of the "stop showing my location"-icon is a bit misleading. Something along the lines of Location disabled might be more to the point.