Add Gen Mass cut for MC ZDefinitions

It can now be specified in the ZDeffintion PSets if the mass cut should
be madd on the Reco mass or the Truth mass.

To help indicate what is being done to the consume of the output data,
the mass cut level name is changed depending on what quantity was used
as follows:
    * Reco:  "... < M_{ee} < ..."
    * Truth: "... < GEN M_{ee} < ..."

Also updated how we make ZDefinitions. Previously we made one set of
ZDefinitions and used these to make two sets of Plots and Workspaces,
one for Truth and one for Reco. We now make two sets of ZDefs, one for
Truth and one for Reco, and use each set to make the corresponding set
of plots.
Update ZDefinitions_cfi with Truth Mass cut option

Allow the user to specify that the mass cut should be made on the Truth
mass.

Added a set of cuts that mirror just the kinematic cuts from our
combined results, in both Generator quantities and Reco.

Also added a set of ZDefinitions without trigger requirements (mainly
for MC without emulated triggers).