Build modified streamline images

The official image from streamline does not currently work for the arm64
platform. As a temporary measure, the source code and docker build scripts
have been lifted from the official images and are used to build locally.

Some additional modifications are made to reduce overall image size, these
are documented in docker/README.md

docker/streamline-src/public/css/font-awesome/scss/_mixins.scss

@@ -0,0 +1,60 @@
+// Mixins
+// --------------------------
+
+@mixin fa-icon() {
+  display: inline-block;
+  font: normal normal normal #{$fa-font-size-base}/#{$fa-line-height-base} FontAwesome; // shortening font declaration
+  font-size: inherit; // can't have font-size inherit on line above, so need to override
+  text-rendering: auto; // optimizelegibility throws things off #1094
+  -webkit-font-smoothing: antialiased;
+  -moz-osx-font-smoothing: grayscale;
+
+}
+
+@mixin fa-icon-rotate($degrees, $rotation) {
+  -ms-filter: "progid:DXImageTransform.Microsoft.BasicImage(rotation=#{$rotation})";
+  -webkit-transform: rotate($degrees);
+      -ms-transform: rotate($degrees);
+          transform: rotate($degrees);
+}
+
+@mixin fa-icon-flip($horiz, $vert, $rotation) {
+  -ms-filter: "progid:DXImageTransform.Microsoft.BasicImage(rotation=#{$rotation}, mirror=1)";
+  -webkit-transform: scale($horiz, $vert);
+      -ms-transform: scale($horiz, $vert);
+          transform: scale($horiz, $vert);
+}
+
+
+// Only display content to screen readers. A la Bootstrap 4.
+//
+// See: http://a11yproject.com/posts/how-to-hide-content/
+
+@mixin sr-only {
+  position: absolute;
+  width: 1px;
+  height: 1px;
+  padding: 0;
+  margin: -1px;
+  overflow: hidden;
+  clip: rect(0,0,0,0);
+  border: 0;
+}
+
+// Use in conjunction with .sr-only to only display content when it's focused.
+//
+// Useful for "Skip to main content" links; see http://www.w3.org/TR/2013/NOTE-WCAG20-TECHS-20130905/G1
+//
+// Credit: HTML5 Boilerplate
+
+@mixin sr-only-focusable {
+  &:active,
+  &:focus {
+    position: static;
+    width: auto;
+    height: auto;
+    margin: 0;
+    overflow: visible;
+    clip: auto;
+  }
+}