Fix build issues and cleanup generated files

This fixes some issues with build.sh which expects certain directories to exists that don't on a fresh checkout and adds redbend_ua and updater-script so that a proper zip can be generated.  It also adds a number of auto-generated files to the ignore list and removes them from Git.

After a ./build captivate command, Git now reports a clean repository as well as after running ./build clean, and after ./build mrproper.