HH-43583 add handler_404 parameter to FileMappingDispatcher
HH-43583 add an example and update docs
Merge remote-tracking branch 'origin/HH-43583' into EXP-11423
release 2.19.17 [an.sumin@hh.ru]
HH-43534 changes for tornado3 upgrade
HH-43534 fix HTTPError and remove HTTPError.xsl
HH-43534 remove apps option