Game polishing: Iteration #2

This pull request contains the following changes:

* Added fancy animation for the Wyvern Rider.
* Added generic enemy emblem for small hover modals.
* Fixed positioning of spawning Equip/Unequip button.
* Added all backgrounds for battle animations.
* Added Assassin "silencer/assassinate" animation background.
* Added a "Miss" animation sheet. 
* Added a "Hit effect" animation sheet.
* Added animations for the new button. It turns dark when pressed down.
* Added generic enemy name to battle summary modal.
* Cleaned up the different fonts from the HP modal. It now generates "HP: # / #" using fonts from Impact. 
* Drew and applied custom image for use in buttons/menus, small modals and character stat screens.
* Removed unused button icons and menu graphics. 
* All battle animation backgrounds are also resized to 640x480.
* Cleaned up the battle animation overlay, it now has a transparent counterpart so that it can be placed over a swappable background image.