Qt Location: add keyboard support to mapview

When using the Qml mapview component on systems with a keyboard (e.g. Windows, Linux, Android with attached keyboard, ...) then map interaction with the keyboard is useful. This can be easily implemented by the end-developer. But the standard behaviour is similar between applications so it might be reasonable to include the support directly in the map component. A flag should be available to disable the keyboard input.

Some input functions are:

• left/right/top/buttom keys to move map around
• +/- to zoom in/out
• Shift+double tap (respectively mouse wheel) zoom out instead of zoom in