Add SAVE button to save plot in GUI mode.

[aditodkar]

Currently the GUI mode does not have any button to SAVE plot.

[realsdx]

I would like to work on this issue

[djmgit]

@realsdx please go ahead :)

[realsdx]

Done.. should i submit a PR ? as my previous PR still not merged.. but i already merged all the branches in my fork

[djmgit]

@realsdx hope you have used a different branch for this change?

[realsdx]

Yes, I have used a different branch... but it also has the quitting problem solved. I need to remove the commit and rebase it as you cannot reproduce it for now.