Modernize XmlTools
identical to !396 (merged), except that it is targeted at future instead of master
- prefer std::unique_ptr with 'release' deleter over raw pointer and explicit call to release
- prefer direct member initialization
- directly use functions from cmath instead of adding a layer of indirection
- remove SVN/CVS keywords
- prefer Gaudi::Property with direct member initialization over declareProperty in c'tor
- prefer passing string by const reference