FR: offset flows to top left and trim grid size

[Steve-Mcl]

To minimise the scrolling a suggestion on the forum was to move the flows to a position top-left and reduce the grid size to better present the the flows.

This would make it obvious if there are other nodes on the workspace since scroll bars would only be present if there are.

Suggested approach:

1. get top-left left most node in a tab & offset all nodes in tab by the same amount
2. get bottom-right most node and resize the grid

This may serve as an alternative to the minimap suggested in #47