Fix includes so that include sorting in clangformat doesn't break anything

[mcarans]

• Fix includes so that include sorting in clang-format doesn't break anything (prior to running clang-format on code)
• Use #pragma once with correct include hierarchy to avoid multiple inclusion of same headers instead of INCLUDED_OOMATHS_h define workaround
• Also we always use OOMATHS_OPENGL_INTEGRATION and !OOMATHS_STANDALONE so remove defines and just have that code always be compiled.
• Remove MacOS non-SDL ifdef in OOOpenGLOnly.h

In my testing with this fix, Oolite compiled and ran successfully before and after running clang-format. Without it, there are compile errors after clang-format due to things not being included correctly.

[mcarans]

@phkb Does this work for you?

[phkb]

All good from me.