I have no idea how bricon <-> display range sync was working at

all. Replaced the old contrast scaling equation with somthing simpler to
invert (and replaced the previously-incorrect inverted scale->contrast
equation). VolumeOpts was incorrectly flipping the resulting bricon
values, as well.

Other small changes - fsldirdlg layout tweak, and ActionButton now does
not require the action to be listed in the strings module.