Provide a warning to implementor when container view has mismatched configuration

[rromanchuk]

Embedding SLKTextViewController in a container view will most likely cause an incorrect bottom margin calculation. Especially when storyboarding as #668

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PR Summary

Scream at user if there is a tabbar inside a container view and its configuration differs from its parent.

Related Issues

Fixes for #668 and #680

Test strategy

NOOP, adds a console warning to potentially reduce headaches. This could and probably be branched, as it's almost never what the implementor intended. Or simply could take the parentViewController's properties when not null (meaning it's in a container). When storyboarding and running, the tabbar isn't shown, and respects the parent's setting, but SlackTextViewController reads this property on the container and provides an incorrect margin making this very difficult to track down and debug.