qFit does not sample backbone if segment is less than 7 residues long

[stephaniewankowicz]

We currently have backbone sampling enabled if there are 3 residues on either side of the residue of interest. This allows the inverse kinematic algorithm to work. But we check if this occurs through qFit segment definition of 'continuous backbone' So if residue 4 is the residue we are working on and it has an alt conf in the backbone, but residue 3 is a single confomer backbone. Because this single conformer backbone splits up the segment, we do not sample the backbone at all (as there are not enough residues on either side).

1. We should be looking for continuous residues just by if they have alpha carbons or not (or all of the backbone, not qFit segment definition.
2. We should enable sampling of backbone to start at multiple spots if the input conformer has multiple positions for the backbone