Keep panel open when clearing the area
Keep panel open when clearing the area

Even if keepVisible is false, the panel should remain if the
panel is cleared of all current content (Trash can icon).

Solves #13

bwinton/atom-build,gregerolsson/atom-build,carmoIn/atom-build,gogoprog/atom-build,5n8ke/atom-build,oli-obk/atom-build,MackieLoeffel/atom-build,e-jigsaw/atom-build,sphaerophoria/atom-build,noseglid/atom-build,tomoasleep/atom-build,jhasse/atom-build,MadcapJake/atom-build,forivall/atom-build