Preserve properties file on save

[aleks-f]

Is your feature request related to a problem? Please describe.
Properties file saving does not preserve comments, includes and the original order of properties.

Describe the solution you'd like
The original file comments, includes and properties order should be preserved.

[matejk]

Closed by #5258

[andrewauclair]

Is this feature always enabled? To prevent this extra save logic from happening do I have to call PropertyFileConfiguration(std::istream& istr); instead of PropertyFileConfiguration(const std::string& path);?

I'm concerned this change is going to cause some serious performance issues due to the std::map<std::string, std::map<std::string, std::string>> fileValues and building up that map of maps every single call to save.

[aleks-f]

It is currently always enabled when the configuration is loaded from a file. The reason (besides the obvious ones: lost comments, reordered entries and merged included files resulting in duplication of configuration content) is that I did not want want to break existing interface for this release. I would not be opposed to adding a bool flag controlling this behavior, defaulting to true.