JSON char > 127 codepage problem

... on the different platforms / QT version the .JSON file was encoding
in different codepages which caused problems for chars > 127
... JSON is now encoded / decoded with UTF-8 codec
... old files containing chars > 127 (e.g. German Umlaut, French chars)
are still properly read and with next update of the JSON file converted
to UTF-8 as well
... t allow external editors to recognize the codec, also the UTF-8 BOM
(Byte Mark Order) is added to the file.