After dragging and dropping a file, the source name will be the
filename.
(Jim: When dragging and dropping raw text, the raw text would then be
used as the source's name, which is bad if there's a lot of text. It's
now been changed so that it uses the source type's display name, i.e.
"Text (GDI+)" as the source name in that case)
Closesjp9000/obs-studio#888