Fixed Last-Modified logick in /get handler

First try to get timestamp from read_result (it is real mtime).
If embed with timestamp exists it overrides value from read_result.
Version up to 2.0.5
Fixed logick in /get /download-info and /delete handlers

Response code is 404 if file does not exist
Version up to 2.0.6
Content type of stat_log was changed to "text/xml"
Version up to 2.0.7