Fix https://savannah.cern.ch/bugs/?93931.

A time axis defined with the GMT option, saved into a root file in a given time zone, was different when displayed in an other time zone. The time zone offset in which the axis was created is now saved with the time axis offset allowing to make the right adjustments when the axis is displayed in an other time zone.


git-svn-id: http://root.cern.ch/svn/root/trunk@44091 27541ba8-7e3a-0410-8455-c3a389f83636