[Feat] GUI: support drag'n'drop of maps

[neteler]

Is your feature request related to a problem? Please describe.

Nowadays some users expect that they can simply "swipe" geodata into the GUI.

Describe the solution you'd like

While this wish may be tough to be implemented, it would already be helpful to "simply" open the respective import dialog GUI window and populate the input field with the path to the map the user wishes to import.

To function, this would require some cascaded tests

• is it a raster map (maybe use gdalinfo functionality (respective Python API)
• is it a vector map (maybe use ogrlinfo functionality (respective Python API)
• is it LAS/LAZ (respective Python API)
• (...)
• is it something else --> tell user to manually select the import tool