Resolve "[wrtier] Remove extra ptsn_ links for timescan"
Closes #1620 (closed)
Simplify the saving of masters with multiple channels like loopscan (epoch and elapsed_time) and a2scan.
Also epoch and elapsed_time are no longer marked as positioners when not timescan or loopscan. They appear as detectors for ascan, amesh , ... (any softtimer triggered scans). For example "a2scan robx ... roby ..." has technically one positioner with four values (robx, roby, epoch and elapsed_time). However it is too messy to figure this out in the writer side so I removed it (was not consistent with the musst either).