Support for includes in yml
Using a single yaml configuration file could become tedious when working with different eras, channels, ... This MR adds support for including the content of a yaml file into another. The syntax is e.g.:
samples: !include samples.yml
where samples.yml
contains the nodes for the different samples as in https://gitlab.cern.ch/swertz/bamboo/blob/master/examples/analysis_zmm.yml#L5