Add border to droparea

[williamtheaker]

It can be kinda hard to see the target for dragging and dropping files. Add something like this maybe to .droparea:
border: dashed 3px gray;
border-radius: 5px;

[ddevault]

The entire window is a valid target for dropping files, actually. Also, an older design had the dashed line (archive.org), but we dropped it later.

I'm open to re-adding the dashed line, though I liked the original look+feel more than the grey dashed line. Anyone else have thoughts? @jdiez17?

[jleclanche]

-1 on the dashed line, never liked it