Change MVA ID variable of electrons to post CMSSW 130X naming

Deals with #60 (closed) Hotfix to allow processing of nanoAOD v12 produced with CMSSW 130X.

(Includes minor comment for photon preselection and one typo fix in prepare output file)

Note

Naming convention for Run 2 ID : `mvaIso_Fall17V2_WPXX

Naming convention for Run 3 ID : mvaIso_WPXX Where XX is 80 or 90.

Run 2 ID supports WPL (Loose) but this is not support anymore for Run 3.