trace_targets nsigma default=10

[simontorres]

the method goodman.pipeline.core.trace_targets which calls the method trace to perform the trace itself, had the nsigmas parameter hard coded to a value of 10, I added an argument nsigma and defaulted it to 10 but I think it might to a bit risky for some kind of data (large binning or targets with wide profile). Anyways it works now but there has to be a method to make this more flexible.