Fix blurry images when UI is scaled > 1x

Fixes blurry rendering for:

• Shortcuts pane
• Icons in list view
• Icons in icon view
• Icons in compact view
• File icon in properties dialog
• Emblems in properties dialog
• Location icon in path bar
• Icons in path bar completion dropdown
• Updated: drag icons
• Updated: gesture icons in file view
• Updated: thumbnails in preview pane

Does not fix:

• Icons in "Open With" chooser dialog (this widget is in libexo: exo!58 (merged))
• Close icon in tab (I don't believe this is actually scaled incorrectly)

Closes #291 (closed).