Make tiles sorting deterministic in all cases

This may fix issue #5916.

In any case, it's wanted because this kind of sort is "unstable".
According to the docs:

    "This implementation performs an unstable sort; that is, if two
    elements are equal, their order might not be preserved."
Fixed typo in HackAI building placement code
Merge pull request #5917 from pavlos256/deterministic-sort

Make tiles sorting deterministic in all cases
Merge pull request #5924 from Cr0s/patch-1

Fixed typo in HackyAI building placement code
Remove bitrotted tab source artwork.
Add opposing-faction tab art for aircraft and navy,
Fix incorrect soviet tab image coordinates.
Enable correct tab images for helicopters and aircraft.
Fix bogus inconsistencies in the ra tab images:

- Soviet-normal tab glyphs were off by 1px.
- Allied-selected tabs had random semi-transparent pixels.
- Most tabs had a discoloured pixel near the left edge.
Sort Changes
Merge pull request #5927 from MustaphaTR/ra-building-sort

Fixes #5914
Merge pull request #5926 from pchote/ra-tabs

Fixes #5915
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. The lifetime for some of these resources is non-trivial so this may not be through, but it's a step in the right direction.

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.