CSV: what agreement looks like

Before judging deadlock, the chain shows what fast agreement looked like on the same field.

2016-04

0.02%

2016-05

26.36%

2016-06

77.47%

2016-08

0.04%

Three months from nothing toward lock-in, then the flag withdrawn. SegWit used the same mechanism and pinned mid-band for seven months instead.