v1.2: Image downloader GUI

• Added a GUI for downloading images.
• Write GeoTIFF files without the GDAL dependency.
• It can also save PNG and JPG with a World File.
• Update the GUI more frequently, so you can cancel the download process.

You can get the "Extent" using the QGIS plugin "Lat Lon Tools".

Precompiled Windows x64 executable (using nuitka) is attached below.