Add blurhash (#10630)

* Add blurhash

* Use fallback color for spoiler when blurhash missing

* Federate the blurhash and accept it as long as it's at most 5x5

* Display unknown media attachments as blurhash placeholders

* Improve style of embed actions and spoiler button

* Change blurhash resolution from 3x3 to 4x4

* Improve dependency definitions

* Fix code style issues

package.json

@@ -78,6 +78,7 @@
     "babel-plugin-react-intl": "^3.0.1",
     "babel-plugin-transform-react-remove-prop-types": "^0.4.24",
     "babel-runtime": "^6.26.0",
+    "blurhash": "^1.0.0",
     "classnames": "^2.2.5",
     "compression-webpack-plugin": "^2.0.0",
     "cross-env": "^5.1.4",