Detect at 5 sigma for deblender

In order to deblend out fainter sources, we probably want to detect deeper
than we need for the final star catalog (which is still S/N>10). Whether this
change is strictly necessary needs to be investigated further.

python/lsst/pipe/tasks/calibrateImage.py

@@ -280,7 +280,7 @@ def setDefaults(self):
         # and do initial detection at S/N>5.0?
         # Detection for good S/N for astrometry/photometry and other
         # downstream tasks.
-        self.star_detection.thresholdValue = 10.0
+        self.star_detection.thresholdValue = 5.0
         self.star_measurement.plugins = ["base_PixelFlags",
                                          "base_SdssCentroid",
                                          "ext_shapeHSM_HsmSourceMoments",