add buttons to zoom in/out and navigate

[HarHarLinks]

zoom is supported by ctrl+scroll or ctrl++/-, but it is not obvious from the ui that you can do that save for the hint of the "reset zoom" button

further you can only navigate by zooming and moving your mouse pointer(?), so that would be nice as well. "go home" needs to be clarified that it means the camera position and not the home page from before choosing a board.