EPUB CFI: Video bookmarking works. Also fix use of coffeescript compiler in threads by deelgating compiling to a worker process, much slower, but doesn't segfault

src/calibre/ebooks/oeb/display/test-cfi/cfi-test.coffee

@@ -32,6 +32,8 @@ window_ypos = (pos=null) ->
 mark_and_reload = (evt) ->
     # Remove image in case the click was on the image itself, we want the cfi to
     # be on the underlying element
+    if evt.button == 2
+        return # Right mouse click, generated only in firefox
     ms = document.getElementById("marker")
     if ms
         ms.parentNode?.removeChild(ms)

src/calibre/ebooks/oeb/display/test-cfi/index.html

@@ -118,10 +118,9 @@
             <p>Try clicking on this video while it is playing. The page should
             reload with the video paused at the point it was at when you
             clicked.  To play the video you should right click on it and select
-            play (otherwise the click will cause a reload). This is currently
-            broken because of issues in the python server use to serve test
-            content. I lack the patience to track down the bug. </p>
-            <video width="320" height="240" controls="controls" preload="auto" src="birds.mp4" type="video/mp4" />
+            play (otherwise the click will cause a reload). 
+            </p>
+            <video width="320" height="240" controls="controls" preload="auto" src="birds.webm" type="video/webm" />
 
         </div>
         <img id="marker" style="position: absolute; display:none; z-index:10" src="marker.png" alt="Marker" />