Update SCSS to module system (fixes #266)

Change-Id: I2387ef49dadaeac0f62620e0c803df12dad42cf8
diff --git a/dev/scss/base/buttongroup.scss b/dev/scss/base/buttongroup.scss
index 1937e53..fc9c6a6 100644
--- a/dev/scss/base/buttongroup.scss
+++ b/dev/scss/base/buttongroup.scss
@@ -1,5 +1,10 @@
 @charset "utf-8";
-@import "../util";
+@use "../util";
+@use "choose";
+@use "colors";
+@use "icons";
+@use "lengths";
+@use "mixins";
 
 /*
  * Define the base layout of horizontal button groups
@@ -15,34 +20,34 @@
     > span,
     input[type=submit],  
     a {
-      @include choose-item;
-      box-shadow:   $choose-box-shadow;
+      @include choose.choose-item;
+      box-shadow:   choose.$choose-box-shadow;
       font-size:    9pt;
       font-weight:  normal;
       line-height:  1.5em;
       padding:      0 4px;
       display:      inline-block;
       border-style: solid;
-      border-width: $border-size 0;
+      border-width: lengths.$border-size 0;
 
       &:not(.inactive):hover {
-	@include choose-hover;
+	@include choose.choose-hover;
         transition: none;
       }
 
       &:first-child {
 	      border: {
-	        left-width:          $border-size;
-	        top-left-radius:     $standard-border-radius;
-	        bottom-left-radius:  $standard-border-radius;
+	        left-width:          lengths.$border-size;
+	        top-left-radius:     lengths.$standard-border-radius;
+	        bottom-left-radius:  lengths.$standard-border-radius;
 	      }
       }
 
       &:last-child {
 	      border: {
-	        right-width:         $border-size;
-	        top-right-radius:    $standard-border-radius;
-	        bottom-right-radius: $standard-border-radius;
+	        right-width:         lengths.$border-size;
+	        top-right-radius:    lengths.$standard-border-radius;
+	        bottom-right-radius: lengths.$standard-border-radius;
         }
       }
     }
@@ -57,21 +62,21 @@
       min-width: auto;
 
       > span.check {
-        @include icon-font;
+        @include mixins.icon-font;
         width:      1em;
         display:    inline-block;
         text-align: left;
 
         &:not(.checked)::after {
-          content: $fa-check;
+          content: icons.$fa-check;
         }
 
         &.checked::after {
-          content: $fa-checked;
+          content: icons.$fa-checked;
         }
 
         > span {
-          @include blind;
+          @include mixins.blind;
         }
       }
     }
@@ -85,12 +90,12 @@
     z-index:   20;
     margin:    0;
     padding:   0;
-    width:     $right-view-distance;
+    width:     lengths.$right-view-distance;
     font-size: 10pt;
-    color:     $nearly-white;
+    color:     colors.$nearly-white;
 
     > span:first-child {
-      margin-top: $border-size
+      margin-top: lengths.$border-size
     }
 
     > span {
@@ -101,19 +106,19 @@
       font-style:      normal;
       
       &.download::after {
-	      content: $fa-download;
+	      content: icons.$fa-download;
       }
       
       &.close::after {
-	      content: $fa-close;
+	      content: icons.$fa-close;
       }
 
       &.minimize::after {
-	      content: $fa-minimize;
+	      content: icons.$fa-minimize;
       }
       
       &.plugin::after {
-	      content: $fa-plugin;        
+	      content: icons.$fa-plugin;        
       }
     }
   }
@@ -126,7 +131,7 @@
   font-size:  10pt;
   left:       0;
   text-align: left;
-  margin:     -1 * $border-size;
+  margin:     -1 * lengths.$border-size;
   margin-top: 0;
 
   > li:first-of-type {
@@ -135,10 +140,10 @@
 }
 
 .button-icon {
-  @include icon-font;
+  @include mixins.icon-font;
   line-height: 1.3;
   > span {
-    @include blind;
+    @include mixins.blind;
   }
   &[data-icon]::after {
     content: attr(data-icon);