places sidebar: keep open variants sensitive
places sidebar: keep open variants sensitive

Add a separate action for "Open in Tab" and "Open in new window"
so we can keep them enabled when we disable "Open" for the selected
row.

https://bugzilla.gnome.org/show_bug.cgi?id=754410

davidgumberg/gtk,jigpu/gtk,jigpu/gtk,jadahl/gtk,grubersjoe/adwaita,grubersjoe/adwaita,alexlarsson/gtk,alexlarsson/gtk,grubersjoe/adwaita,davidgumberg/gtk,grubersjoe/adwaita,grubersjoe/adwaita,jadahl/gtk,alexlarsson/gtk,jigpu/gtk,grubersjoe/adwaita,jigpu/gtk,grubersjoe/adwaita,jadahl/gtk,jigpu/gtk,jigpu/gtk,davidgumberg/gtk,davidgumberg/gtk,jadahl/gtk,jadahl/gtk,grubersjoe/adwaita,davidgumberg/gtk,davidgumberg/gtk,davidgumberg/gtk,alexlarsson/gtk,jigpu/gtk,jadahl/gtk,alexlarsson/gtk,jigpu/gtk,alexlarsson/gtk,alexlarsson/gtk,jadahl/gtk,alexlarsson/gtk,jadahl/gtk,davidgumberg/gtk