Add test for NLog properties in Log4JXmlEvent
add context properties to to Nlog data section of Log4JXmlEventLayoutRenderer
Fix writing NLog properties in Log4JXmlEvent

The pull request provided only wrote NLog properties when including
CallSite or SourceInfo. Move the rendering of the properites out so
properties will be written when including NLogData, even if CallSite or
SourceInfo aren't included