Flip structure extracts for reverse strand ScanFolds

[rjandr]

For each extracted structure in the extracted structure list, if strand == reverse, flip the coordinates as the gff file is written.

[njbooher]

from #31 #32

For ScanFold RNAfold the reverse strand extracted structures still appear to be flipped for visible and selected scans.

[rjandr]

Put some potential fixes in commit 6de4b64