Add Rallpack1 validation, plus bugfix, clean

* Implement Rallpack1 validation test (with a workaround
  for inability to set membrane conductance).
* Fix bug in L≠1 case in PassiveCable.jl (this may still be
  wrong).
* Fix bug in peak delta computation in trace analysis when
  both traces have no local maxima.
* Gentle failure on missing `numeric_soma.json`
* Allow multiple `-s` selection operations for `tsplot`,
  acting disjunctively.