Track frequently used emojis in web UI (#5275)

* Track frequently used emojis in web UI

* Persist emoji usage, but debounce commits to the settings API

* Fix #5144 - Add tooltips to picker

* Display only 2 lines of frequently used emojis

package.json

@@ -45,7 +45,7 @@
     "css-loader": "^0.28.4",
     "detect-passive-events": "^1.0.2",
     "dotenv": "^4.0.0",
-    "emoji-mart": "^2.1.1",
+    "emoji-mart": "Gargron/emoji-mart#build",
     "es6-symbol": "^3.1.1",
     "escape-html": "^1.0.3",
     "express": "^4.15.2",