fix form switch changed callback

Add yad-form-switch@GtkSwitch to manual page

Here this example showed garbage when the switch widget was changed
```sh
yad --form --field=switch:SW TRUE --field=check:CHK TRUE --changed-action='echo 3:' --field=changes
```
To fix this issue I changed the callback according to the gobject signature https://docs.gtk.org/gobject/signal.Object.notify.html.

add missing form field types

yad-settings.in: fix get -> set

configure.ac: fix typo