[libQGLViewer] FIX missing headers

[gKevin]

We ran into some more compile errors on windows using MSVC 2015.

libQGLViewer wouldn't compile without those missing headers.

Here's a quick fix but you might want to update libQGLViewer to the latest version (2.7.0).

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This PR:

• builds with SUCCESS for all platforms on the CI.
• does not generate new warnings.
• does not generate new unit test failures.
• does not generate new scene test failures.
• does not break API compatibility.
• is more than 1 week old (or has fast-merge label).

Reviewers will merge only if all these checks are true.

[sofabot]

Thank you for your pull request!
Someone will soon check it and start the builds.

[guparan]

Thanks @gKevin. I set this PR as fast-merge.
[ci-build]