PATCH: Graphincal explain integrated in sql editor

Hi Team,

PFA the first patch for graphical explain integrated in sql editor.

Below are the few things which are different from previous patch which was
sent for stand alone graphical explain.

- Now user can select Explain/Explain Analyze with four optional
properties (Verbose, costs, timing and buffers)

- Initially graph will be scale (according to only its width not height)
to fit to screen so no blank space will be there in case of very large
graph.

- Along with zoom in/out button, "zoom to original" button is also
provided, by clicking on which graph will be scale to its original size
(not same as initial one which is according to screen size).

Please do review this patch and let me know in case you have any comments.

Regards,
Sanket Mehta
Sr Software engineer
Enterprisedb