additional SFramework features: explicit counter values, Norm factor filters, POI properties

Release notes

A few features have been added:

• TQSampleDataReader can now retrieve counters with explicit values given as paths (getCounter("1.","TheCutName"))
• TSModelBuilder can now filter NormFactors with Include and Exclude statements
• NormFactors can now be flagged as POI=true

Closes #396 (closed)