JBST is a start theme and not a framework. WordPress has a structure to build child themes. The main purpose of child theming is its ability to upgrade the parent theme easily. JBST 4 is intended to be used as a starter theme, not as a parent or theme framework. In almost all instances, it is recommended you just hack away and customize JBST 4 itself as described in this chapter.
You can run Bower to keep Bootstrap's code and its dependencies up to date.