Hide points and crosshairs

[Carolyn Eng]

It can be hard to tell if the point tracking is working if the tracked marker is hard to see in the image and this is made more difficult if it's covered up by the crosshairs. It would be useful if when tracking points, a point and its crosshairs could be hidden temporarily to check that the marker is being tracked correctly.

[Benjamin Knorlein]

put a shortcut for disable drawing.

[Benjamin Knorlein]

fixes #109, #110, #100 : Added more DisplayOptions in extra dockwidget and refactored the toolbox to use icons

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