Use 'touch' instead of 'mobile'

Using touch as a variable name instead of mobile as this is what we are
testing for.

h/static/scripts/annotator/guest.coffee

@@ -13,8 +13,8 @@ module.exports = class Guest extends Annotator
     "document onselectionchange": "userSelectionChanged"
 
   # We bind different events depending on whether the browser supports touch.
-  mobile = 'ontouchstart' in window or window.DocumentTouch and document instanceof DocumentTouch
-  if mobile
+  touch = 'ontouchstart' in window or window.DocumentTouch and document instanceof DocumentTouch
+  if touch
     # This hack is needed for iOS Safari.
     $(window).bind 'selectionEnd', ->
       # reset selection timeout
@@ -209,7 +209,7 @@ module.exports = class Guest extends Annotator
   _setupViewer: -> this
   _setupEditor: -> this
   _setupDocumentEvents: ->
-    if not mobile
+    if not touch
       $(document).bind({
         "mousedown": @checkForStartSelection
       })

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

@@ -5,8 +5,10 @@ class Annotator.Plugin.TextSelection extends Annotator.Plugin
     @Annotator = Annotator
     @$ = Annotator.$
 
+    touch = 'ontouchstart' in window or window.DocumentTouch and document instanceof DocumentTouch
+
     # Register the event handlers required for creating a selection
-    if /Android|webOS|iPhone|iPad|iPod|BlackBerry|IEMobile|Opera Mini/i.test(navigator.userAgent)
+    if touch
       $(document).bind({
         "touchend": @checkForEndSelection
       })

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

@@ -12,18 +12,17 @@ makeButton = (item) ->
 class Annotator.Plugin.Toolbar extends Annotator.Plugin
   PUSHED_CLASS = 'annotator-pushed'
 
-  mobile = 'ontouchstart' in window or window.DocumentTouch and document instanceof DocumentTouch
+  touch = 'ontouchstart' in window or window.DocumentTouch and document instanceof DocumentTouch
 
   events:
     'setVisibleHighlights': 'onSetVisibleHighlights'
 
   html: '<div class="annotator-toolbar"></div>'
 
   pluginInit: ->
-    # On mobile, we don't hide the toolbar.
     @annotator.toolbar = @toolbar = $(@html)
-    if mobile
-      # When there is a selection on mobile show/hide highlighter
+    if touch
+      # When there is a selection on touch devices show/hide highlighter
       document.addEventListener "selectstart", ->
         if window.getSelection().toString() != ""
           annotator.plugins.Toolbar.showHighlightButton(false)
@@ -103,7 +102,7 @@ class Annotator.Plugin.Toolbar extends Annotator.Plugin
       $(@buttons[1]).children().addClass('h-icon-visibility-off')
 
   _updateStickyButtons: ->
-    # The highlight button is hidden except when there is a selection on mobile
+    # The highlight button is hidden except when there is a selection on touch devices
     if $(@buttons[3]).css('display') == 'none'
       height = 105
     else height = 140