add 'Skip' button to overwrite dialog for dirs

add 'Skip' button to overwrite dialog for dirs

When overwriting directory with another directory, 'No' would mean to
skip it altogether. But it should mean only not to overwrite the files
inside, but move those that are not there. Thats how it works now, and
there is a 'Skip' button that will skip the directory altogether.

Signed-off-by: Lukas Hrazky <lukkash@email.cz>