Migrate server to ESM

Sorry for the very big commit that may lead to git log issues and merge
conflicts, but it's a major step forward:

 * Server can be faster at startup because imports() are async and we can
   easily lazy import big modules
 * Angular doesn't seem to support ES import (with .js extension), so we
   had to correctly organize peertube into a monorepo:
    * Use yarn workspace feature
    * Use typescript reference projects for dependencies
    * Shared projects have been moved into "packages", each one is now a
      node module (with a dedicated package.json/tsconfig.json)
    * server/tools have been moved into apps/ and is now a dedicated app
      bundled and published on NPM so users don't have to build peertube
      cli tools manually
    * server/tests have been moved into packages/ so we don't compile
      them every time we want to run the server
 * Use isolatedModule option:
   * Had to move from const enum to const
     (https://www.typescriptlang.org/docs/handbook/enums.html#objects-vs-enums)
   * Had to explictely specify "type" imports when used in decorators
 * Prefer tsx (that uses esbuild under the hood) instead of ts-node to
   load typescript files (tests with mocha or scripts):
     * To reduce test complexity as esbuild doesn't support decorator
       metadata, we only test server files that do not import server
       models
     * We still build tests files into js files for a faster CI
 * Remove unmaintained peertube CLI import script
 * Removed some barrels to speed up execution (less imports)

packages/tests/src/shared/mock-servers/mock-email.ts

@@ -0,0 +1,62 @@
+import MailDev from '@peertube/maildev'
+import { randomInt } from '@peertube/peertube-core-utils'
+import { parallelTests } from '@peertube/peertube-node-utils'
+
+class MockSmtpServer {
+
+  private static instance: MockSmtpServer
+  private started = false
+  private maildev: any
+  private emails: object[]
+
+  private constructor () { }
+
+  collectEmails (emailsCollection: object[]) {
+    return new Promise<number>((res, rej) => {
+      const port = parallelTests() ? randomInt(1025, 2000) : 1025
+      this.emails = emailsCollection
+
+      if (this.started) {
+        return res(undefined)
+      }
+
+      this.maildev = new MailDev({
+        ip: '127.0.0.1',
+        smtp: port,
+        disableWeb: true,
+        silent: true
+      })
+
+      this.maildev.on('new', email => {
+        this.emails.push(email)
+      })
+
+      this.maildev.listen(err => {
+        if (err) return rej(err)
+
+        this.started = true
+
+        return res(port)
+      })
+    })
+  }
+
+  kill () {
+    if (!this.maildev) return
+
+    this.maildev.close()
+
+    this.maildev = null
+    MockSmtpServer.instance = null
+  }
+
+  static get Instance () {
+    return this.instance || (this.instance = new this())
+  }
+}
+
+// ---------------------------------------------------------------------------
+
+export {
+  MockSmtpServer
+}