Chore/convert to typescript (#60)

* Convert to using TypeScript

Next.js v.9 allows converting an existing project to TS by simply renaming the files as TS files

* Fix type errors: Type 'string' is not assignable to type 'number'.

* Add mention about missing typings for javascript-time-ago

* Add GA_INITIALIZED to window

* Fix type error in feed transformers

* Model MembershipInfoForm state and props with TS

* Silence the typescript warning in MembershipInfoForm

* Add threshold to Fader props

* Fix Warning: Each child in a list should have a unique "key" prop.

Sponsors don't have ids – name is probably unique and can be used as a key

* Allow key as prop for SponsorLink

* Add type of the props for SponsorLink

package-lock.json

@@ -1089,6 +1089,28 @@
       "resolved": "https://registry.npmjs.org/@csstools/convert-colors/-/convert-colors-1.4.0.tgz",
       "integrity": "sha512-5a6wqoJV/xEdbRNKVo6I4hO3VjyDq//8q2f9I6PBAvMesJHFauXDorcNCsr9RzvsZnaWi5NYCcfyqP1QeFHFbw=="
     },
+    "@types/node": {
+      "version": "12.12.5",
+      "resolved": "https://registry.npmjs.org/@types/node/-/node-12.12.5.tgz",
+      "integrity": "sha512-KEjODidV4XYUlJBF3XdjSH5FWoMCtO0utnhtdLf1AgeuZLOrRbvmU/gaRCVg7ZaQDjVf3l84egiY0mRNe5xE4A==",
+      "dev": true
+    },
+    "@types/prop-types": {
+      "version": "15.7.3",
+      "resolved": "https://registry.npmjs.org/@types/prop-types/-/prop-types-15.7.3.tgz",
+      "integrity": "sha512-KfRL3PuHmqQLOG+2tGpRO26Ctg+Cq1E01D2DMriKEATHgWLfeNDmq9e29Q9WIky0dQ3NPkd1mzYH8Lm936Z9qw==",
+      "dev": true
+    },
+    "@types/react": {
+      "version": "16.9.11",
+      "resolved": "https://registry.npmjs.org/@types/react/-/react-16.9.11.tgz",
+      "integrity": "sha512-UBT4GZ3PokTXSWmdgC/GeCGEJXE5ofWyibCcecRLUVN2ZBpXQGVgQGtG2foS7CrTKFKlQVVswLvf7Js6XA/CVQ==",
+      "dev": true,
+      "requires": {
+        "@types/prop-types": "*",
+        "csstype": "^2.2.0"
+      }
+    },
     "@webassemblyjs/ast": {
       "version": "1.8.5",
       "resolved": "https://registry.npmjs.org/@webassemblyjs/ast/-/ast-1.8.5.tgz",
@@ -2942,6 +2964,12 @@
         }
       }
     },
+    "csstype": {
+      "version": "2.6.7",
+      "resolved": "https://registry.npmjs.org/csstype/-/csstype-2.6.7.tgz",
+      "integrity": "sha512-9Mcn9sFbGBAdmimWb2gLVDtFJzeKtDGIr76TUqmjZrw9LFXBMSU70lcs+C0/7fyCd6iBDqmksUcCOUIkisPHsQ==",
+      "dev": true
+    },
     "cyclist": {
       "version": "1.0.1",
       "resolved": "https://registry.npmjs.org/cyclist/-/cyclist-1.0.1.tgz",
@@ -10318,6 +10346,12 @@
         "is-typedarray": "^1.0.0"
       }
     },
+    "typescript": {
+      "version": "3.6.4",
+      "resolved": "https://registry.npmjs.org/typescript/-/typescript-3.6.4.tgz",
+      "integrity": "sha512-unoCll1+l+YK4i4F8f22TaNVPRHcD9PA3yCuZ8g5e0qGqlVlJ/8FSateOLLSagn+Yg5+ZwuPkL8LFUc0Jcvksg==",
+      "dev": true
+    },
     "ua-parser-js": {
       "version": "0.7.20",
       "resolved": "https://registry.npmjs.org/ua-parser-js/-/ua-parser-js-0.7.20.tgz",