Changing bootcamp to workshop

This PR replaces the term "bootcamp" with the term "workshop" in filenames and internally, but leaves old blog posts alone.  It also modifies `_htaccess` to redirect `/bootcamps` to `/workshops`.
@gvwilson should we use `<a href="{{page.root}}/workshops/">workshops</a>` instead of `<a href="{{page.root}}/bootcamps/">boot camp</a>`?