Reduce HWrapper interface and switch plotting to accessors.

This is for singular (on a per event basis) quantities only for now.
Quite some plots need fixing still.
Remove GetJetIndex(), which has been obsolete since v48.
Add accessor code generation for methods defined in the Branches headers.
Improve plotting.

Adds channel specific plots, better naming matching, and reduction of
obsolete stuff.
Prepare for plotting arrays.
Fix weights and combination selection for dilepton.
Improve configuration for dilepton.
Add python bits for reduced HWrapper interface.
Remove obsolete bits from branches.
Add more bits for plotting vectors.
Merge branch 'branch_get_attr'

Conflicts:
	interface/Process.h
	scripts/copy_histograms