Fixed bug of 2nd algorithm/animation failing with crash.
This was due to the assumption of DisjointSet that
all vertex will have id starting from 0 in sequence.
This is not true, because user could have deleted a vertex,
or this could be a second animation run.
In this case, this assumption is not right, and this doesn't
work with 0-based array in action in DisjointSet.

Quick fix is to reset the id of the vertex (normalize)
right before the algorithm run.
Now, we can export/import graph into file!
Made necessary changes to Edward's implementation.
Also, we now present file open/save as dialog
as we export/import graph data.
Merge pull request #22 from karpark/MoreUIWork

Wired Graph Export/Import feature into the panel