yad-settings.in: fix get -> set

configure.ac: fix typo

Run image changed hook after image load

...key press when no image is loaded

Runs after image file is selected via gtk_file_chooser_dialog
yad --picture --file-op --image-changed="echo %s

now it is in common section and works in html and picture dialogs too
this option is required now to add open action in popup menu of html dialog

add --changed-action handler to switch field in form dialog