Changed extension to use editor tab/space settings for JSON.stringify()

Hi Stephen

I have updated the extension to use the editors settings. This way if I have tabs setup and a team mate has space, we get the desired results when we run this to clean up JSON.

I also moved it from the file menu to the edit menu. It is not opening or saving files and all other extensions I have that reformat a file currently reside in the edit menu. Therefor it made more sense to me to move it. I also changed the string that was placed on the menu as it has no spaces or formatting. Feel free to change the wording.

Simon