Add 2D (pt vs eta) tracking efficiency plot ot IDPVM output

Adds a tracking efficiency vs pT vs eta plot to the IDPVM output. This is needed for creating inputs to the Track TruthFilter Tool. The output histogram uses the finest binning in existing tool input (100 MeV binning for pT). This is to allow flexibility in the variable rebinning used to prepare the input for InDetTrackTruthFilterTool.

Also adds functionality to book 2D TEfficiency objects to the IDPVM plotting framework. If the XML definition contains an nBinsY attribute for the y-axis, then a 2D TEfficiency object is created. If it does not, then a 1D TEfficiency object is created. Note that the y-axis definition does not seem to have any effect for 1D TEfficiency objects in the current implementation.