Follow the song in the lyrics

Synced LRC highlights the playing line, keeps it centred and seeks on click.
Plain text scrolls continuously with a nudge knob instead — a highlight on
guessed timings turns guaranteed drift into what looks like a bug. Seuraa
kappaletta turns following off without losing the highlight, and scrolling by
hand turns it off too.

Fixes the scroll landing in the wrong place (offsetTop measured from a
different coordinate space than the box it was applied to) and the fader
shifting the deck sideways at score 100 (auto-sized grid columns plus a
readout spanning both).

templates/song.html

@@ -53,11 +53,8 @@
       <!-- Two panes when the song has lyrics: read on the left, write on the right, so following
            the words costs no scrolling. Without lyrics the pane is absent, not empty. -->
       <div class="panes{{if not $s.Lyrics}} solo{{end}}">
-        {{with $s.Lyrics}}
-          <div class="lyricspane">
-            <span class="cap">Sanoitukset</span>
-            <div class="lyricsbox">{{lyricstext .}}</div>
-          </div>
+        {{if $s.Lyrics}}
+          <div class="lyricspane">{{template "lyricsview" $s}}</div>
         {{end}}
         <div class="writepane">
           <label class="grow">Arvostelu