New variable must not overlap previously created variables

[daemontus]

When adding a new variable by clicking a button (not double click into the editor), the variable is always created at (0,0). This is bad because the created variables overlap. Create new variables at positions that do not overlap.

Possible solution: Run through all objects in the graph and compute average y coordinate and max x coordinate. Then place the variable at (y, x + delta). This will add new variables in a "row" right next to the rest of the graph.