PLT-2816 Fixed handling of Unicode 8 emojis (#2924)

* Updated twemoji to properly recognize Unicode 8.0 emojis

* Updated unicode emoji parser to only render emojis we support as images

* Corrected filename for South African flag emoji

* Added Mattermost emoticons!

* Added additional emoticons to test files

webapp/package.json

@@ -29,7 +29,7 @@
     "react-router": "2.0.1",
     "react-textarea-autosize": "3.3.0",
     "superagent": "1.8.3",
-    "twemoji": "1.4.1",
+    "twemoji": "2.0.5",
     "velocity-animate": "1.2.3"
   },
   "devDependencies": {