Staff filter shouldn't search nearby y values

Previously, the staff filter refined the y-value estimate, and only
kept the single-pixel refined line. However, this undermines the Hough
transform since we could actually have a rhores-wide line.
Therefore, it made the center line less prominent, and the line above
or below it could be detected if there are prominent ledger lines.
Change staff filter algorithm

Lines should only contribute to the y center estimate if the entire
run is contained +- staff_thick*2.
Don't calculate boundaries for structure
Fixed affine transformation out of bounds
Flexible barline width
Reduce staff line search space
crap
Fixed matching thick barlines

There is a small regression with note stems being misidentified as barlines.