Renderer cleanup

[mfigueirido]

This PR addresses:

• Removal of unused code.
• Cleaning of newlines/indentation and other small styling fixes.
• Used var for local references when appropriate (following MS guidelines primitive types like bool shouldn't use var).
• Maintained existing comments but updated a few that no longer made sense or were obsolete.
• Removed instances where the code accessed a list element by index in many places instead of caching the current loop object.
• Merged Renderer.Common into Renderer.
• Fixed a few member access inconsistencies.
• Categorized fields, properties and methods into easier to follow regions and sorted methods by order of usage.
• Changed variables naming from mVariables into _variables.
• Renamed DrawableBatch.cs to IDrawableBatch.cs.

[vchelaru]

Thanks so much!