Make toolbox for marker tracking more compact

[Elizabeth Brainerd]

The words can be more compact in the buttons and that would help with small screens. Maybe change the labels for the sections to

Track Point previous frame next frame backward forward

Track Selected Points previous frame next frame backward forward

Track All Points previous frame next frame backward forward

Interpolation Update Active Update All

[Benjamin Knorlein]

fixes #90 : Reduced size of Toolbox for tracking

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