Add stable history detection using ROC test

[nhey]

There are two versions of mhistory_roc, one is more close in style to the existing futhark code (map represents a single kernel). Probably should merge only one of them.

The futhark code needs to b retuned and tuning must be reenabled (L126, bfast/monitor/opencl/base.py). I am leaving this undone for now.