Improved asset loading and simplified rendering

[SoggyRhino]

Description

Renderer and Mesh changes

• Separation of concerns since there is a Render class it makes more sense for it to handle binding buffers/textures and drawing
• Render can better handle opengl state avoiding state checks inside a mesh render function
• Trimmed unnecessary opengl calls

SpriteSheet

• Potential NullPointerException if ImageIO.read() throws
• Added all code into a single catch block since it is all being handled the same way
• SpriteSheet(String filename) is never used but I wasn't sure if it is for future imporvemts

Layer

• Cache Images to avoid reading the same file from disk multiple times
• Resulted in a significant improvement on startup speed

Type of change

• Bug fix (non-breaking change which fixes an issue)
• [ ✓] New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Checklist:

• [✓ ] I have performed a self-review of my own code
• [ ✓] I have commented my code, particularly in hard-to-understand areas
• [ X] I have added tests that prove my fix is effective or that my feature works