Made gdi04c easier to win and added cell trigger guards
Move Utils.Seconds and .Minutes into DateTime global

Also renames Date.IsHalloween to DateTime.IsHalloween
Move Utils.CenterOfCell into Map global
Point out pitfalls in the Lua API documentation
Whitespace fixes
Remove more references to old Lua API

Fixes #6811
Merge pull request #6807 from obrakmann/lua-cleanups

Lua cleanups
Dispose of graphics resources deterministically.

Textures, FrameBuffers and VertexBuffers allocated by the Sdl2 Renderer were only being released via finalizers. This could lead to OpenGL out of memory errors since resources may not be cleaned up in a timely manner. To avoid this, IDisposable has been implemented and transitively applied to classes that use these resources.

As a side-effect some static state is no longer static, particularly in Renderer, in order to facilitate this change and just for nicer design in general.

Also dispose some bitmaps.
Clean up style of files affected by the last commit.