Refactoring animations, small bug fix

This pull request contains the following changes:

* Redid 4 animation sheets for thief, monk, assassin and myrmidon. 
* Refactored all animations into base_player, and removed animations from all player entities.
* Removed old animation sheets.
* Fixed bug where the player would always critical if their crit_rate was > 1. For example, when the slim sword is equipped, the player has 5.5 critical. Since Math.random( ) rolls between 0 and 1, it will always trigger a critical hit.