Fixed out of range bug in FindSigmaMin and added check.

In ToolBox.py:
- made output of FindSigmaMin quieter (like other fit optimisations)
- tidied FindSigmaMin
- old limit for EtaCorrection sigma finding was being hit for thicker sensors.
Increased limit and added a check to warn user is limit is hit again.
- and in ComputeEfficiency, added returns to output file text