css: refactor timeslider

- simplify template
- use flexboxes
- simplify javascript code
- remove some obsolete code adjusting a background-position when using steppers buttons
- add comments and remove old code

src/static/js/broadcast.js

@@ -125,7 +125,7 @@ function loadBroadcastJS(socket, sendSocketMsg, fireWhenAllScriptsAreLoaded, Bro
         }
         else
         {
-          $("#padcontent").prepend(newDivs[i]);
+          $("#innerdocbody").prepend(newDivs[i]);
         }
         startDiv = newDivs[i];
       }
@@ -548,12 +548,12 @@ function loadBroadcastJS(socket, sendSocketMsg, fireWhenAllScriptsAreLoaded, Bro
   {
     // set up the currentDivs and DOM
     padContents.currentDivs = [];
-    $("#padcontent").html("");
+    $("#innerdocbody").html("");
     for (var i = 0; i < padContents.currentLines.length; i++)
     {
       var div = padContents.lineToElement(padContents.currentLines[i], padContents.alines[i]);
       padContents.currentDivs.push(div);
-      $("#padcontent").append(div);
+      $("#innerdocbody").append(div);
     }
     debugLog(padContents.currentDivs);
   });