Adding screens, updating animations

This pull request has the following:

* Added a new level. It's currently a beta level.
* Adding images for player/enemy phase screen transitions.
* Hooked up the enemy Wyvern Lord with its corresponding animation. Also made the Wyvern Lord animation frames bigger.
* Hooked up Assassin critical hit animation. 
* Fixed bug where hovering over a unit during the battle shows HP Modals. This still happens during the fade out transition, so I'll look into that.