[BUG] Walk / Run movement modifiers are buggy

[skaldarnar]

The player is supposed to be able to toggle between running and walking with the Shift modifier key, and to permanently toggle the movement mode with Capslock. Using these modifier keys can lead to state where the player is stuck in one movement mode.

This is currently broken due to the way NUI handles the built-in tabbing feature, and the way this handling is interpreted in Terasology as consuming the key event.

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Related to MovingBlocks/TeraNUI#37

Part of #2573