add --alsoplaceholder option

Details:
this option can be useful now that our WZ reference sample (126893) is
a placeholder. Example:
./python/submitJobs.py --susyplot -s 'Sherpa_CT10_lllnu_WZ' -t Oct_01 \
 --alsoplaceholders -o -S
move ProgressPrinter to a separate file

Details:
- move ProgressPrinter def/impl from SusyPlotter to ProgressPrinter
- move ProgressPrinter from SusyPlotter to SusySelection
use progress printer
cacheStaticWeights, not just reset
drop m_ET state variable
SusySelection: call computeNonStaticWeightComponents

Details:
this now brings SusySelection in sync with SusyPlotter (same weighted
cutflow for WZ)
Merge pull request #12 from gerbaudo/progress-printer

note to self: WZ yields
Dilepton type    :         ee        mm        em        me     em+me 
ht               :        336       492       382       283       665
metRel           :        168       492       182       138       320

weighted
ht               :    5.90385    29.699   11.3782   8.87536   20.2536
metRel           :    2.53355    29.699   5.16486   4.88203   10.0469