Added sprites and rendering code for Justin and other minor changes

- Enemy.java
- added attribute size and its getter method
- updated constructor for the new attribute size
- removed abstract method render()

- Justin.java
- Increased SIZE
- added static attributes for storing textures and animations
- added methods for loading textures and updating current frame

- World.java
- set enemy state to idle only if current state was inactive

- WorldRenderer.java
- draw collision blocks only when debug mode is turned on
- added code to render enemy sprites

- Other Changes:
- created separate directories for different textures
- Renamed textures.pack, textures.png to BobAndMap.pack, BobAndMap.png
- Added justin textures
- Added code to pack textures for Justin with Bob and Map textures