add class 'completed' to any step that comes before the 'active' step

[donalfenwick]

Adds a completed class to any step before the 'active' step.

This allows for styling the previous steps and adjacent connecting lines as described in issue #87

.completed { background-color: green; }
.completed + .bs-stepper-line, .completed + .line { background-color: green; }

[ghost]

use .bs-stepper-header .active .bs-stepper-circle { background-color: #ffff; border: 2px solid #57BC80; } .bs-stepper-header div:not(.bs-stepper-header .active ~ div, div.active, .parent :first-child) { .bs-stepper-circle { background-color: #57BC80; border: 2px solid #57BC80; }}