Add borderColor option to tasks.

I'd like to have borders around some of my tasks. This increases the number of color combinations I can use to display a task.

For example: Task 1 is Red background, and Task 2 is White background with Red border. The meaning is that they are related tasks.

Thoughts?

You probably won't accept this as-is. I'd rather not do a ton of re-writing, so I'd be happy if this serves only as an idea or as a reference.