cmscore-less subs no longer break KO
added export script
added batch-merge-subtitles
corrected export.pl signature
removed 'nepřehrává se' from JS
added formatted current-filestem observable
fixed button checks
auto-bookmarking

- hitting play button without choosing a file now restores previous playback;
- only when no bookmark is set, a random file is chosen;
- m.reached_media_end() now tracks if the media reached its end;
- if so, no bookmark is set;
- ctrl-space now also calls play button's callback;