Alexander Mikhaylenko authored Aug 02, 2019 and Guido Gunther committed Aug 05, 2019

The dtd file is very old and doesn't match gtk+.xml from glade gtk plugin.

Update it so that the future additions pass verification.

---

Add add-child-verify-function, add-child-function, remove-child-function,
replace-child-function, child-action-activate-function,
get-property-function, verify-function, special-child-type and
packing-actions to glade-widget-class element definition.

Additionally define add-child-verify-function,
child-action-activate-function, get-property-function, special-child-type,
and packing-actions elements.

For packing-action, define action element and attributes.

Define and add displayable-values to property definition.

Remove parameter-spec's duplicate "paremter-spec" and add min child,
along with its definition.