add more photon fields
add new IRB models to electron-pair production
update of CRPropa-data required
add IRB models to photo-pion production
requires to pull from crpropa3-data
refactor photo-disintegration to use total cross section and branching ratios and add IRB models to it
requires updating from CRPropa3-data
fix new Observer scheme
rename SourceProperty to SourceFeature
rename Source::addProperty to Source::add
replace some == 0 against < numeric_limits::min()
CMakeLists: adding XmlExecute.cpp to CRPROPA_SOURCES breaks the unit tests
As globbing is not recommended for the source files, return to listing all source files
refactoring PD and EPP
fix testInteractions after changes to various interaction modules
Use cmake to obtain data files from crpropa.desy.de
crpropa-data repository is now obsolete