Add help button to stan editor - open user guide

[magland]

Close #192

[jsoules]

Looks good to me. Only thing to consider is making the help button the same blue color as the other icons in the toolbar--wasn't sure if the difference was intentional (to make it stand out) or not.

[magland]

Looks good to me. Only thing to consider is making the help button the same blue color as the other icons in the toolbar--wasn't sure if the difference was intentional (to make it stand out) or not.

I was just being consistent with the help buttons on the data script editors. If others have a preference it doesn't matter to me.

[WardBrian]

I think we can consider colors as part of #186, for now I agree matching the others is good