fontinfo.plist import/export v4. update for PR 215

see https://github.com/metapolator/metapolator/pull/215
ok so it seems that {} works for an empty plist. I'll update for that case in the catch.

        var pl = {};
        var r = plistLib.createPlistString( pl );


gives for r

    <?xml version="1.0" encoding="UTF-8"?>
    <!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd"><plist version="1.0"><dict/></plist>