Add easy way to pause dialog

[Jowan-Spooner]

Although get_tree().paused works, there are moments where you want to pause the dialog but not the rest of the game.

Pausing should affect:

• [x] Input
• [x] Text revealing + Voice
• [x] Portrait Animations
• [ ] Sounds/Music

Proposal:

We should add a pause() and unpause() method to the DialogicGameHandler (the autoload) This method should then call optional methods in all subsystems so they can manage their pausing and unpausing.