Fixed caching issue for generating subtitle mapping, now it should restart efficiently.
Now ignoring subtitle counts, b/c this is unique to central server.
Added exception to improve ensure_dir util.
Integrated some intermittent updating of srt availability and fixed a bug with the paths of the files.
new_only now renamed as 'existing videos'.  No update is actually done.
Merge branch 'subtitles_immediate_fix' of github.com:dylanjbarth/ka-lite into subtitles_immediate_fix