ADDED: UI - UILayoutSystem that creates and resizes a root panel that spans the whole screen.
ADDED: UI - Horizontal and vertical anchors.
ADDED: UI - Removing labels and anchors if their respective entities are removed.
ADDED: UI - New class UIFactory for conveniently creating UI entities.
CHANGED: UI - Refactored code for creating UI panels from UILayoutSystem to UIFactory.
FIXED: Math - Default Vector2F and RectF constructors correctly initialize objects to zero.
ADDED: UI - Creating sprites with UIFactory and rendering them with RenderSystem.
ADDED: UI - Anchoring widgets to each other.
ADDED: UI - Anchoring widgets centered.
ADDED: UI - Introduced new interface IRenderable implemented by labels and sprites.
CHANGED: UI - Renamed TextData class to Label and moved it from Rendering to UI namespace.
ADDED: UI - Depth sorting of UI widgets.
CHANGED: UI - Cleaned up UI factory to make creation of UI widgets more modular.
ADDED: UI - Inheriting depth of panels.
ADDED: UI - Panels can be anchored.
ADDED: UI - Showing and hiding UI widgets.
ADDED: UI - Inheriting panel visibility.
FIXED: Math - Syntax error in MathUtils.
ADDED: UI - Hit testing for buttons, including depth testing.
FIXED: UI - Layout system correctly removes anchors whose entities have been removed.