dE/dx calibration 2015 pp200 (T0 update)

 After T0 correction the dE/dx resolution for 2014 pp200 sample is slightly improved
(RunXV11 is before T0 correction, RunX19 after it). 
http://www.usatlas.bnl.gov/~fisyak/star/PiD/RunXV/Res_Before_11_and_After_19_T0_Correction.png

Work on averaged TPC power supply table is continued.