Add bootstrap 3 variable shim

app/assets/stylesheets/framework.bs3.scss

+$text-color: $gl-text-color;
+
+$brand-primary: $gl-primary;
+$brand-success: $gl-success;
+$brand-info: $gl-info;
+$brand-warning: $gl-warning;
+$brand-danger: $gl-danger;
+
+$border-radius-base: 3px !default;
+
+$modal-body-bg: $white-light;
+$input-border: $border-color;
+$input-border-focus: $focus-border-color;

app/assets/stylesheets/framework.scss

 @import "framework/variables";
 @import "framework/mixins";
 @import "../../../node_modules/bootstrap/scss/bootstrap";
+@import "framework.bs3";
 @import "framework/layout";
 
 @import "framework/animations";