Improve handling of runArgs.inputGeneratorFile

Description of bug

!2902 (merged) introduced a very strict check disallowing all mentions of runArgs.inputGeneratorFile in a jO. As a result a syntax like this

Herwig7Config.lhef_powhegbox_commands(lhe_filename=runArgs.inputGeneratorFile,me_pdf_order="NLO", usepwhglhereader=True)

was flagged as an error, while it shouldn't be.

Changes introduced

Only check if a jO contains

runArgs.inputGeneratorFile = 

(with an optional number of tabs and spaces before and after the =)

Tests

With file from !3043 (merged)

Issues resolved

Closes #