[RFE] Allow selecting an iso by drag and drop from a file explorer

[dreua]

I love the GUI and simplicity of it, but selecting an existing iso to burn is still a bit of work. (I like to use the torrents for Fedora ISOs and occasionally burn a non Fedora iso.)

Transmission has a handy "open folder" function so dragging the iso from there into FME would work very nicely.

Slightly related: I opened #347 some time ago thinking it could be the easiest way to select an external iso via command line parameters.

[dreua]

Current behavior: It seems to implement no drop locations, I tried it in the main screen and in the screen with the "select" button.