7.3 - Flight model improvements / Additional effects

This update is focused on cleaning up the flight models, adding some additional visual treats, and some behind the scenes maintenance to get the project ready for missions and weather systems (as well as the Godot 4.3 upgrade).

Visual and Gameplay Updates:

1. Rotor wash is now added! You will see dirt and debris kick up when close to the ground, which scales with your rotor RPM as well.
2. Tweaked flight models to bring characteristics more in line with each aircraft's real-world counterparts.
3. Added pictures and more detailed descriptions of each aircraft in the selection screen
4. *Not quite a good thing* Removed trees, as the plugin I was using (ProtonScatter) was too heavy to scale to the size world I needed. Once Terrain3D adds it's own scatter solution, I will re-implement this.

Internal Updates:

1. Refactored much of the code in the foundational scripts to better prepare for world states, weather, and missions in the future
2. Cleaned up code; improvements removed upwards of 200 lines of inefficient scripting (I'm getting better!). The game is a bit snappier and should feel better in the menus and in-game.
3. In preparation for Godot 4.3, removed C# plugins that weren't essential and switched off of the mono version. This should allow a cleaner and easier path forward once the upgrade hits.

Overall, I'm very happy with this update, which should perform much more consistently and better on all hardware. Thanks for reading!