timeline_list.tx, timeline_list.js: update Timeline list table.
Now it has separate cells for "total" counts, and a <thead> header row.
timeline_list.js: fix bug that UnackedCountsRenderer did not empty the old counts.
timeline_list.js, busybird.css: prevent word-wrap inside "level : unacked_count" pairs, for improved visibility.
timeline_list.js, timeline_list.tx: in top-view, now per-level unacked counts are rendered as list.
timeline.js: unacked counts pairs in status summary now have "white-space: nowrap" style so that the pair is never split.