Hi background subtraction

This includes changes which allow the use of the HI-style background subtraction with the UCT2015 emulator. Care was taken to avoid making any changes to the other algorithms, so existing code should require no modifications and the output for the other algorithms should remain the same. 

The details of the HI algorithm are included in the first commit message below.

I have added a boolean flag to EfficiencyTree.cc to allow us to force the Vertex information off; this was necessary for HI data which uses a different format for the vertex and where we often assume that there is only one vertex. "useVertex" defaults to true

I have added a boolean flag to UCT2015Producer.cc to allow the use of the HI algorithm. "useHI". It defaults to "false" in emulation_cfi.py.