Implement Page404File and Page500File and their handler, tidy up ShowRequestException
Improved Page404 and Page500 handlers
# Improved exception display.
# Updates broker unit generator.
# Updates the broker unit of all demos.
Updates Page404File and Page500File settings for '.html' templates in demos.
Updated Page404 handler to get '@path'
TBrookQuery.JSONToFields/TBrookQuery.JSONToParams: fixes erroneous command.
Merge branch 'working'