Track trending tags (#7638)

* Track trending tags

- Half-life of 1 day
- Historical usage in daily buckets (last 7 days stored)
- GET /api/v1/trends

Fix #271

* Add trends to web UI

* Don't render compose form on search route, adjust search results header

* Disqualify tag from trends if it's in disallowed hashtags setting

* Count distinct accounts using tag, ignore silenced accounts

package.json

@@ -97,6 +97,7 @@
     "react-redux-loading-bar": "^2.9.3",
     "react-router-dom": "^4.1.1",
     "react-router-scroll-4": "^1.0.0-beta.1",
+    "react-sparklines": "^1.7.0",
     "react-swipeable-views": "^0.12.3",
     "react-textarea-autosize": "^5.2.1",
     "react-toggle": "^4.0.1",