Added detailed error message. Refs #7789.
Modified 2 log output to information. Refs #7789.

The reason to change them from warning to information is that
GetDetOffsetsMultiPeak() will call Fit() millions of time in a typical
calibration.  There is no way to hide warning log in MantidPlot.
Made a series minor changes including ... .  Refs #7789.

1. Corrected discrpencies in cost function name;
2. Refactored logging in class FitOneSinglePeak;
3. Added debug output
Merge branch 'feature/7789_fitpeak_to_findpeaks_new' into develop