Consistently ignore default Locale, and format using WLocale
- We should not use any function that may be affected by the current locale (e.g. do not use boost::lexical_cast)
- We should support proper formatting in WItemDelegate, WAxis also if a format string is given:
- let WLocale embrace std::locale, and read grouping separator, etc... from the corresponding facet?
- we could still support the setters, see also: https://stdcxx.apache.org/doc/stdlibug/25-5.html
- do number formatting/parsing using boost::format ?