Instrument sequentials with segment-io so we know when people switch tabs…

Instrument sequentials with segment-io so we know when people switch tabs manually or using the arrows to navigate

common/lib/xmodule/xmodule/js/src/sequence/display.coffee

@@ -111,6 +111,11 @@ class @Sequence
     if (1 <= new_position) and (new_position <= @num_contents)
       Logger.log "seq_goto", old: @position, new: new_position, id: @id
 
+      analytics.track "Sequential Goto",
+        old: @position
+        new: new_position
+        id: @id
+
       # On Sequence chage, destroy any existing polling thread
       #   for queued submissions, see ../capa/display.coffee
       if window.queuePollerID
@@ -127,12 +132,22 @@ class @Sequence
     Logger.log "seq_next", old: @position, new: new_position, id: @id
     @render new_position
 
+    analytics.track "Sequential Next",
+        old: @position
+        new: new_position
+        id: @id
+
   previous: (event) =>
     event.preventDefault()
     new_position = @position - 1
     Logger.log "seq_prev", old: @position, new: new_position, id: @id
     @render new_position
 
+    analytics.track "Sequential Previous",
+        old: @position
+        new: new_position
+        id: @id
+
   link_for: (position) ->
     @$("#sequence-list a[data-element=#{position}]")