Move all the map widget platform agnostic files to the
<subsurface-root>/map-widget folder.
This avoids the confusion about the desktop version of subsurface
using mobile components. The map widget is planned as a shared
component between the mobile and desktop versions.
desktop-widgets/mapwidget[.h/.cpp] still remain as those are specific
to the desktop version.
Signed-off-by: Lubomir I. Ivanov <neolit123@gmail.com>
