Refresh the emoji library (#7001)

* refresh the emoji library

* fix img_trans.gif

* compress sprite sheet

* remove note on compression - webpack seems to handle compression decently

* better emoji sheet preloading

* requested changes

webapp/i18n/en.json

@@ -1335,14 +1335,14 @@
   "emoji_picker.custom": "Custom",
   "emoji_picker.emojiPicker": "Emoji Picker",
   "emoji_picker.flags": "Flags",
-  "emoji_picker.food": "Food",
+  "emoji_picker.foods": "Foods",
   "emoji_picker.nature": "Nature",
   "emoji_picker.objects": "Objects",
   "emoji_picker.people": "People",
   "emoji_picker.recent": "Recently Used",
   "emoji_picker.search": "Search",
   "emoji_picker.symbols": "Symbols",
-  "emoji_picker.travel": "Travel",
+  "emoji_picker.places": "Places",
   "error.local_storage.help1": "Enable cookies",
   "error.local_storage.help2": "Turn off private browsing",
   "error.local_storage.help3": "Use a supported browser (IE 11, Chrome 43+, Firefox 38+, Safari 9, Edge)",