JSON char > 127 codepage problem (Issue #1028)

... on the different platforms/QT version the .JSON ridefile was encoded using different (local) codepages which caused problems with chars > 127 (since the local encoder of QT changed in QT5 for some platform)
... .JSON is now always encoded/decoded with UTF-8 codec
... old files which contain chars > 127 (e.g. German Umlaut, French accent?) are still decoded with Latin1/ISO8859-1) codec if the decoding in UTF-8 failed for some chars
... the UTF-8 files get the respective BOM (Byte order mark) added, so that any editor being able to handle unicode can recognize the code page