Introduces `common.djangoapps.util.log_sensitive module` for public-key encryption of sensitive debug information in log messages, including CLI commands for generating keys and decrypting log output. Also: - Adds `PyNaCl` to base requirements for encryption tools - Requirements upgrade ref: ARCHBOM-1940
common ------ This directory contains common code shared between LMS and CMS, such as Mako templates, CSS, and Coffescript.