GSASII initial guess reflection peak fit

[DanielMurphy22]

The override unit cell values are used to match the reflections to the peaks. These reflections are generated in mantid. Saurabh would like a peak fit where a user can check how the initial guess of unit cell matches reflections with the raw data peaks. This "fitting" should probably act a little like the initial guess in the fit property browser.

This feature would allow the user to give the best initial guess to GSASII.