refactor(Sidebar): add variables to set .nav-group-items paddings

Author: mrholek

scss/_variables.scss

@@ -1871,9 +1871,12 @@ $sidebar-nav-icon-font-size:               $sidebar-nav-icon-height !default;
 
 $sidebar-nav-group-bg:                     rgba(0, 0, 0, .2) !default;
 $sidebar-nav-group-transition:             background .15s ease-in-out !default;
-$sidebar-nav-group-items-transition:       height .15s ease !default;
 $sidebar-nav-group-toggle-show-color:      $sidebar-nav-link-color !default;
 
+$sidebar-nav-group-items-padding-y:        0 !default;
+$sidebar-nav-group-items-padding-x:        0 !default;
+$sidebar-nav-group-items-transition:       height .15s ease !default;
+
 $sidebar-nav-group-indicator-color:        $medium-emphasis-inverse !default;
 $sidebar-nav-group-indicator-icon:         url("data:image/svg+xml,<svg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 16 16' fill='#{$sidebar-nav-group-indicator-color}'><path fill-rule='evenodd' d='M1.646 4.646a.5.5 0 0 1 .708 0L8 10.293l5.646-5.647a.5.5 0 0 1 .708.708l-6 6a.5.5 0 0 1-.708 0l-6-6a.5.5 0 0 1 0-.708z'/></svg>") !default;
 $sidebar-nav-group-indicator-hover-color:  $sidebar-nav-link-hover-color !default;

scss/sidebar/_sidebar-nav.scss

@@ -100,6 +100,7 @@
     @include transition($sidebar-nav-group-transition);
 
     .nav-group-items {
+      padding: $sidebar-nav-group-items-padding-y $sidebar-nav-group-items-padding-x;
       overflow: hidden;
       @include transition($sidebar-nav-group-items-transition);
     }