Solve #1323: refresh and store subtitles in the location where 0.10.2 servers can download & access them.  Also, make central and distributed server-accessible srt paths the same.
Only write files if some subtitle info has been changed; otherwise, skip those time-consuming steps.
Add client-side download code, fix bug.
Fix display of subtitles.
Merge pull request #1337 from bcipolli/1323

Update subtitles paths on central and distributed servers, to be consistent with past versions (and each other)