Create a basic version of the tower placing UI (closes #37)

Assets/Scenes/Simulation.unity

Assets/Scripts/Presentation/UI/SimulationUI.cs

Assets/Scripts/Presentation/UI/TowerPlacingUI.cs

Assets/Scripts/Presentation/UI/UnitDeploymentUI.cs

Assets/Scripts/Presentation/World/SimulationCamera.cs

Assets/UI/Simulation/GameUISTyles.uss

Assets/UI/Simulation/GameUISTyles.uss.meta

Assets/UI/Simulation/TowerPlacing.meta

Assets/UI/Simulation/TowerPlacing/TowerPlacingUI.uxml

Assets/UI/Simulation/TowerPlacing/TowerPlacingUI.uxml.meta

Assets/UI/Simulation/UnitDeployment/UnitDeploymentUI.uxml

Assets/World/Structures/Towers/EmptyTowerType.asset