Add BLT workflow

# First attempt at BLT (aka LGBT) workflow.

The ```makeBLT_cfg.py``` config is based partly on the unfolding workflow and partly on the makeTuples workflow.  The full selection is applied, as in the unfolding workflow, with the ntuple output as in the makeTuples workflow.  With the following changes:

**Modified collections** - the jets that end up in the ntuple are the cleaned collections, as produced by the selection filters
**New collections** - these ntuples contain the global event variables, as calculated in AnalysisSoftware.  These are calculated using the (cleaned) jets and signal leptons as produced by the selection filters.

**The output file contains two trees**, one for the electron/muon channel.  Also, the cleaned jet collections are different between the two channels, so the jet and global event variable modules are run twice in the workflow with different input collections.

**RootTupleMakerV2_Tree** has a new parameter 'treeName', so the name of the tree in the output file can be changed i.e. different names for electron tree and muon tree.  Its default value is 'tree', so should be ok for existing workflows.