Preferences.voice sustain

I allowed a user to determine whether voices were sustained through the current interaction.

I added three actions.
         * Preference("voice sustain", "enable")  - Sustain voice through the current interaction.
         * Preference("voice sustain", "disable") - Don't sustain voice through the current interaction.
         * Preference("voice sustain", "toggle")  - Toggle sustain voice.
And I used all_character_callbacks to implement this future.
Default to False