KF jet selection bug fix

Kinematic Fit bug causing jobs to fail is fixed (easyjet/issues/#273). The container of the additional jets in KF takes into account both the additional b-jets and the nob-jets, but there is also a >6 central jets cut to save computational resources (and in line with the legacy analysis cut; KF is optimized for 0,1,2,3 add cen jets). The current number of central jets is calculated only taking into account the nob-jets, but in the situation where there are >2 b-jets (like the loose analysis configuration, with which the job bug was found) the total number of central jets is the sum of the additional b-jets + central nob-jets.