Clean up unused and duplicate TextHighlight code

This commit is intended as a pure refactoring. No behaviour should be
changed.

h/static/scripts/annotator/plugin/bucket-bar.coffee

@@ -84,7 +84,7 @@ class Annotator.Plugin.BucketBar extends Annotator.Plugin
               acc
           , {}
 
-          next.paddedScrollDownTo()
+          next.paddedScrollTo('down')
           delete @pendingScroll
 
     @annotator.subscribe "highlightRemoved", (highlight) =>

h/static/scripts/annotator/plugin/enhancedanchoring.coffee

@@ -83,12 +83,6 @@ class Anchor
       # Kill the list if it's empty
       delete @anchoring.anchors[index] unless anchors.length
 
-  # This is called when the underlying Annotator has been udpated
-  annotationUpdated: ->
-    # Notify the highlights
-    for index in [@startPage .. @endPage]
-      @highlight[index]?.annotationUpdated()
-
 Annotator.Anchor = Anchor
 
 # This plugin contains the enhanced anchoring framework.
@@ -107,13 +101,6 @@ class Annotator.Plugin.EnhancedAnchoring extends Annotator.Plugin
 
     this
 
-  # Sets up handlers to anchor-related events
-  _setupAnchorEvents: ->
-    # When annotations are updated
-    @annotator.on 'annotationUpdated', (annotation) =>
-      # Notify the anchors
-      for anchor in annotation.anchors or []
-        anchor.annotationUpdated()
 
   # Initializes the components used for analyzing the document
   _chooseAccessPolicy: ->
@@ -161,7 +148,6 @@ class Annotator.Plugin.EnhancedAnchoring extends Annotator.Plugin
     @selectorCreators = []
     @strategies = []
     @_setupDocumentAccessStrategies()
-    this._setupAnchorEvents()
 
     self = this
     @annotator.anchoring = this

h/static/scripts/annotator/plugin/textrange.coffee

@@ -62,7 +62,7 @@ class Annotator.Plugin.TextRange extends Annotator.Plugin
   # Create a RangeSelector around a range
   _getRangeSelector: (selection) =>
     return [] unless selection.type is "text range"
-    sr = selection.range.serialize @annotator.wrapper[0], '.' + @Annotator.TextHighlight.highlightClass
+    sr = selection.range.serialize @annotator.wrapper[0], '.annotator-hl'
     [
       type: "RangeSelector"
       startContainer: sr.start

h/static/scripts/annotator/plugin/textselection.coffee

@@ -88,9 +88,8 @@ class Annotator.Plugin.TextSelection extends Annotator.Plugin
 
     for range in selectedRanges
       container = range.commonAncestor
-      # TODO: what is selection ends inside a different type of highlight?
-      if @Annotator.TextHighlight.isInstance container
-        container = @Annotator.TextHighlight.getIndependentParent container
+      if @$(container).hasClass('annotator-hl')
+        container = @$(container).parents(':not([class^=annotator-hl])')[0]
       return if @annotator.isAnnotator(container)
 
     if selectedRanges.length