Order of nodes should reflect time based 1st appearance

[yoosiba]

For a specific flow, graph nodes should be shown in order of in which participate in a give flow. So graph layout algorithm should take first appearance (time based) of the node as the input, i.e. chronological order should be preserved.

For example wen flow was 1->2, 2->3, 2->4, 4->5
Order of nodes (either left to right, or top down, or whatever arbitrary direction) should be 1, 2, 3 and 4, 5, e.g.

1 -> 2 -> 3 
      \-> 4 -> 5