The ad-hoc labelling used here forces us to use the check box’s
actual content as a description, removing the mnemonic underscore
chars and working around an Orca bug.

This will only read the icon name when a system icon is
used; in case of custom icons a generic “Icon” label is
read instead of the full path.

This commit adds a function to libcaja, as it will be
useful elsewhere down the line.

This implies creating an empty focusable widget so that its
mnemonic label will be read when pressing Tab.

This whole window should be rewritten as a
GtkDialog with standard buttons.

Otherwise there would be no way to leave that text area without
using the mouse.