make more strings translatable

admin/templates/users.php

apps/media/appinfo/app.php

apps/media/js/collection.js

apps/media/js/music.js

apps/media/js/playlist.js

apps/media/js/scanner.js

apps/media/l10n/xgettextfiles

apps/media/templates/music.php

core/css/styles.css

core/js/js.js

core/l10n/xgettextfiles

core/templates/layout.user.php

files/appinfo/app.php

files/js/filelist.js

files/js/files.js

files/l10n/xgettextfiles

files/templates/index.php

files/templates/part.list.php

l10n/templates/admin.pot

l10n/templates/core.pot