Build, sign, notarise, & upload on OS X (#687)

* sign & notarise darwin package

* upload bundle as github release

* allow unsigned build and full build with release

* deref darwin bundle symlinks only when building on win32

Windows [mangles symlinks](https://github.com/electron/electron-packager/issues/71). Currently we work around this by placing several copies of the frameworks in OS X app bundles (see 1e5aa3867d). However:

- This is invalid: the framework toplevel must [only contain symlinks](https://developer.apple.com/library/archive/documentation/MacOSX/Conceptual/BPFrameworks/Concepts/FrameworkAnatomy.html). `codesign` [refuses to sign](https://stackoverflow.com/questions/25969946/osx-10-9-5-code-signing-v2-signing-a-framework-with-bundle-format-is-ambiguou) this invalid structure.

- It seriously bloats the bundle.

Since there's no fix for the Windows misbehaviour, keep the workaround, but only when cross-building on win32 for darwin; and log a warning.

gulp/gulpfile.js

@@ -42,6 +42,10 @@ const envVars = [
     "SHAPEZ_CLI_STAGING_FTP_PW",
     "SHAPEZ_CLI_LIVE_FTP_USER",
     "SHAPEZ_CLI_LIVE_FTP_PW",
+    "SHAPEZ_CLI_APPLE_ID",
+    "SHAPEZ_CLI_APPLE_CERT_NAME",
+    "SHAPEZ_CLI_GITHUB_USER",
+    "SHAPEZ_CLI_GITHUB_TOKEN",
 ];
 
 for (let i = 0; i < envVars.length; ++i) {
@@ -78,6 +82,9 @@ docs.gulptasksDocs($, gulp, buildFolder);
 const standalone = require("./standalone");
 standalone.gulptasksStandalone($, gulp, buildFolder);
 
+const releaseUploader = require("./release-uploader");
+releaseUploader.gulptasksReleaseUploader($, gulp, buildFolder);
+
 const translations = require("./translations");
 translations.gulptasksTranslations($, gulp, buildFolder);
 
@@ -299,6 +306,17 @@ gulp.task(
     gulp.series("utils.cleanup", "step.standalone-prod.all", "step.postbuild")
 );
 
+// OS X build and release upload
+gulp.task(
+    "build.darwin64-prod",
+    gulp.series(
+        "build.standalone-prod",
+        "standalone.prepare",
+        "standalone.package.prod.darwin64",
+        "standalone.uploadRelease.darwin64"
+    )
+);
+
 // Deploying!
 gulp.task(
     "main.deploy.alpha",