Fixed incorrect flag image files for subtitle languages

gui/slick/images/flags/ar.png

gui/slick/images/flags/ay.png

gui/slick/images/flags/bg.png

gui/slick/images/flags/bs.png

gui/slick/images/flags/ca.png

gui/slick/images/flags/cs.png

gui/slick/images/flags/da.png

gui/slick/images/flags/de.png

gui/slick/images/flags/el.png

gui/slick/images/flags/en.png

gui/slick/images/flags/es.png

gui/slick/images/flags/et.png

gui/slick/images/flags/fa.png

gui/slick/images/flags/fi.png

gui/slick/images/flags/fr.png

gui/slick/images/flags/he.png

gui/slick/images/flags/hi.png

gui/slick/images/flags/hr.png

gui/slick/images/flags/hu.png

gui/slick/images/flags/hy.png