Add alert message component and documentation

- Add custom alert component to simplify the use of custom alerts
- Add documentation for using the custom alert
- Update the login error alert to use the alert component instead of
the Bootstrap-vue component.
- Register alert component in enhanceApp
- Replace Sass variables used in the StatusIcon component style block
to use the Boostrap theme-color and gray Sass functions so the colors
can be used in the Vuepress documentation custom components

Signed-off-by: Derick Montague <derick.montague@ibm.com>
Change-Id: Ibd93402c919a42bd5c24cc9e7c6c8fc6f17a4db4
diff --git a/docs/.vuepress/config.js b/docs/.vuepress/config.js
index 680c98e..a07000e 100644
--- a/docs/.vuepress/config.js
+++ b/docs/.vuepress/config.js
@@ -44,6 +44,7 @@
             title: "Components",
             children: [
             "/guide/components/",
+            "/guide/components/alert",
             "/guide/components/button",
             "/guide/components/toast",
           ]