Update the stitching GUI specifying the Q range index other curve stitching to

We got some initial feedback on the curve stitching tool in the stitching GUI. A couple of suggestions:

1 In stitching of curves from multiple q ranges, there is one curve that others scale to (usually the first Q range), and curves that will be scaled to the main one. The instrument scientists want to be able to specify which curve to scale to (the benchmark q range index number)

2 The instrument scientists want to show the scale factors of each curve during stitching, like what is the multiplication applied to each q range

3 They also want Q min Q max for the whole curve after stitching (in the third plot of the stitching page), so that data before and after Q min Q max will be truncated (you may make them gray or dashed).

The usual work flow, accordingly, is stitch, and trim low Q and high Q unstable data, and export the whole Q curve. They do not want to switch to another application just for trimming.

These requests should be desired by both BioSANS and GPSANS users.