Add code for dilepton and quadruplet angles

[rsamconn]

First step is to figure out what variables are needed. Candidates are:

1. Opening angle between leptons in a pair
2. Opening angle between the vectors of two pairs
3. Phi/ eta of a pair (sum of phi/eta of each lepton? Or average?)
4. Phi/eta of the quadruplet (same questions as for a pair)

[rsamconn]

For now, ignore leading/subleading, e/u and angles between pairs/ individual leptons.

Simply go for: l1l2 eta + phi l3l4 eta + phi 4l eta + phi

[rsamconn]

• [x] Add histograms to .h file
• [x] Add histogram checks (to .cxx file in initialize() section)
• [x] Add new variables (to .cxx file between initialize() and execute() sections)
• [x] Add lines to save variables for each event (to .cxx file, in execute() kinematics section)
• [x] Fill histograms (in .cxx file, execute() bitmask section)