MacOS compatibility issues

[Ermelber]

Problem

You cannot load courses in MKTB under MacOS for some reason related to the main window's width and height preventing the proper creation of the GL framebuffer.
Furthermore, having a different retina scales causes more issues such as not being able to click items correctly and other scaling mismatches.

Error info

   at HaroohiePals.Gui.Viewport.Framebuffers.GLCompleteFramebuffer..ctor(GLFramebufferDefinition definition, Int32 width, Int32 height)
   at HaroohiePals.Gui.Viewport.Framebuffers.TestGLFramebufferProvider.CreateFboMulti(Vector2i size)
   at HaroohiePals.Gui.Viewport.Framebuffers.TestGLFramebufferProvider.BeginRendering(Int32 width, Int32 height)
   at HaroohiePals.Gui.Viewport.ViewportPanel.DrawGL()
   at HaroohiePals.Gui.Viewport.ViewportPanel.Draw()
   at HaroohiePals.MarioKartToolbox.Gui.View.CourseEditor.CameraPreviewView.Draw()
   at HaroohiePals.MarioKartToolbox.Gui.View.CourseEditor.CourseEditorContentView.<>c.<Draw>b__28_0(IView x)
   at System.Collections.Generic.List`1.ForEach(Action`1 action)
   at HaroohiePals.MarioKartToolbox.Gui.View.CourseEditor.CourseEditorContentView.Draw()
   at HaroohiePals.Gui.ImGuiViewWindow.RenderLayout(FrameEventArgs args)
   at HaroohiePals.Gui.ImGuiGameWindow.OnRenderFrame(FrameEventArgs args)
   at OpenTK.Windowing.Desktop.GameWindow.DispatchRenderFrame()
   at OpenTK.Windowing.Desktop.GameWindow.Run()
   at HaroohiePals.MarioKartToolbox.Program.Main(String[] args)
Abort trap: 6