Ignore regions outside mask in barrel finder

[pmknutsen]

Barrel finder locates putative zones of intrinsic activation in loaded .dat files. Often, however, acquired frames also include regions outside of the cranial/thin-skull window which may covered in reflective dental acrylic. Zones in these regions are often picked out by barrel finder. When a mask has been selected (manually or otherwise), the region outside the net mask should be ignored by barrel finder to limit such false positives.