Added pflow variables to the IsolationCorrectionTool

Hi,

@schaffer noticed that in the case of Pflow isolation the correction was not always piped properly. This is fixed now by this MR -- which is the smaller and easier part of the changes-- The remaining changes address improvements of the validation macros to check the performance of the correction.

To convince yourself that the correction is actually doing what is meant for please have a look at these two set of plots: Vanilla isolations Corrected isolations

C.C: @szambito, @fsforza, @oducu, @maklein, @jmiguens, @jshahini, @sakatsuk, @lveloce, @sabidi and our well admired friend the @atlasbot