[TMP] Fix Sass dependencies import for Bower

⚠️ **This is a temporary solution**

Unlike NPM, Bower does not have its own registry and uses the Github
repository. Like `js, `sass` and `dist`, all the files required by
Bower must be published on Git.

Changes:
- Pin the Sass dependencies versions and update `yarn.lock`
- Move only the require files to `/vendor`
- Publish the Sass dependencies in `vendor/` on git.

.gitignore

@@ -15,7 +15,6 @@
 .sass-cache/*
 .yardoc
 _build
-_vendor
 .customizer
 
 bower_components

_vendor/normalize-scss/sass/_normalize.scss

@@ -0,0 +1,3 @@
+@import 'normalize/variables';
+@import 'normalize/vertical-rhythm';
+@import 'normalize/normalize-mixin';

_vendor/normalize-scss/sass/normalize/_import-now.scss

@@ -0,0 +1,11 @@
+// Import Now
+//
+// If you import this module directly, it will immediately output all the CSS
+// needed to normalize default HTML elements across all browsers.
+//
+// ```
+// @import "normalize/import-now";
+// ```
+
+@import '../normalize';
+@include normalize();