Include powheg input cards, minor changes in the create_powheg_tarball.sh and runcmsgrid_powheg.sh

Changes include:
1) Remove the file setupPowheg.sh
2) Include a directory "example" that stores examples of powheg data cards
3) create_powheg_tarball.sh: rename the output tar ball so to be consistent with the name used in run_generic_tarball.sh, retrieve runcmsgrid_powheg.sh from GIT instead of from work directory
4) runcmsgrid_powheg.sh: remove the requirement of "withnegweights 1" in the powheg input card