Add hidden threads count on the index.

src/Filtering/ThreadHiding.coffee

@@ -24,7 +24,29 @@ ThreadHiding =
       else unless root.contains thread.stub
         # When we come back to a page, the stub is already there.
         ThreadHiding.makeStub thread, root
-    return
+    ThreadHiding.updateToggle()
+  updateToggle: ->
+    hiddenCount = 0
+    for threadID, thread of g.BOARD.threads when thread.isHidden
+      hiddenCount++ if thread.ID in Index.liveThreadIDs
+    unless hiddenCount
+      ThreadHiding.removeToggle()
+      return
+    unless ThreadHiding.toggler
+      ThreadHiding.addToggle()
+    $('#hidden-count', Index.navLinks).textContent = if hiddenCount is 1
+      '1 hidden thread'
+    else
+      "#{hiddenCount} hidden threads"
+  addToggle: ->
+    ThreadHiding.toggler = $.el 'span',
+      id: 'hidden-label'
+      innerHTML: ' &mdash; <span id="hidden-count"></span>'
+    $.add Index.navLinks, ThreadHiding.toggler
+  removeToggle: ->
+    return unless ThreadHiding.toggler
+    $.rm ThreadHiding.toggler
+    delete ThreadHiding.toggler
 
   syncCatalog: ->
     # Sync hidden threads from the catalog into the index.
@@ -157,6 +179,7 @@ ThreadHiding =
     return if thread.isHidden
     threadRoot = thread.OP.nodes.root.parentNode
     thread.isHidden = true
+    ThreadHiding.updateToggle()
 
     unless makeStub
       threadRoot.hidden = threadRoot.nextElementSibling.hidden = true # <hr>
@@ -171,3 +194,4 @@ ThreadHiding =
     threadRoot = thread.OP.nodes.root.parentNode
     threadRoot.nextElementSibling.hidden =
       threadRoot.hidden = thread.isHidden = false
+    ThreadHiding.updateToggle()