Adds an action object to the action group and sets up the accelerator.
If accelerator is NULL, attempts to use the accelerator associated
with the stock_id of the action.
Accel paths are set to
<Actions>/group-name/action-name.
Since 2.4
the accelerator for the action, in
the format understood by gtk_accelerator_parse(), or "" for no accelerator, or
NULL to use the stock accelerator. [allow-none]
Adds an action object to the action group and sets up the accelerator. If accelerator is NULL, attempts to use the accelerator associated with the stock_id of the action. Accel paths are set to <Actions>/group-name/action-name. Since 2.4