Fix on TRestMetadata and TRestDataSet add-ons

[jgalan]

TRestMetadata::GetDataMemberValues minor fix on TVector2,3 output component

Before this PR (for the case of TVector2,3), the following output was generated when invoking GetMetadataMember.

root [7] run0->GetMetadataMember("axionGen::fEnergyRange[0]")
(std::string) "(0.05"
root [8] run0->GetMetadataMember("axionGen::fEnergyRange[1]")
(std::string) "10)"

After this PR, parenthesis are removed from the output.

root [7] run0->GetMetadataMember("axionGen::fEnergyRange[0]")
(std::string) "0.05"
root [8] run0->GetMetadataMember("axionGen::fEnergyRange[1]")
(std::string) "10"

Added also:

• REST_Generate_DataSets macro that will allow to export several datasets from a given list of dataset names.
• Added new filter condition equalsTo that allows to evaluate numerically if a datamember is equal to the filter. If it is not equal, then the run will be rejected and thus not included in the dataset.
• Added method TRestDataSet::Define that allows to create a new column using the values of relevant quantities.
• Added method TRestDataSet::Import( std::vector <std::string> fNames ) allowing to combine datasets into one single instance. If saved to disk the metadata member fMergedDataSet will be true in order to identify that it is a non-pure original dataset.

For the moment metadata filter conditions do not support units. See issue: #429

[jgalan]

I am going a need an Import method that allows me to combine different datasets to be loaded in TRestComponent. Thus, I have implemented a new Import method allowing to receive several ROOT files as argument. There will be a datamember fMergedDataSet that keeps track if this method was used to initialize the dataset.

I also added a new TRestDataSet::Define method that allows to generate a new column using/replacing the values of relevant quantities.

Any feedback about their implementation? @juanangp