Add scrolling up and down

[kelemeno]

When the graph grows too large, we will not be able to display all of it. Especially on phones. The easiest solution is to only display part of the graph and to add scrolling up and down the graph. This would happen with buttons.

Scrolling up can only go one way, for downward we pick a direction.

We could also add the clickedNode functionality to this, the clickedNode could never be at the edge of the displayed graph (except when it is on the edge of the whole graph).

We have to check what size can we display at most. This could be different for different screens.

[kelemeno]

We could also change the visualization details on different screens. E.g. nodeRadiu=small in DrawGraph for phones.