[ feature request ] support drag&drop for image-import

[GralfR]

Hi!

Inserting an image into a label is a quite long way: select image-tool, add image-object, then browse for a file, reset the image-object to get a correct aspect ratio, then enable the checkbox to keep aspect ratio on scaling, and finaly scale and position the image. I think this could be faster, if one could browse for a file inside the systems file browser (which would support bookmarks and network-shares, too; see #152) and just drag&drop that image into the label-editor. That procedure should:

• create an image-object at the position the file was dropped
• assign the dropped file to that image-object
• the image-object should have the 100% size and correct ratio of the dropped file
• the checkbox "keep ratio" should be checked on that dropped image-object

Thanks