Refactor author usage into WP_Stream_Author class; use System user always
Fix assignment alignment issue for PHPCS
Use Unknown user instead of System user
Fix coding style to use elseif
Use N/A instead of Unknown
Remove unused variable
Introduce author agent concept and logging WP Cron

See #431
Change some variable names
Code formatting
Merge branch 'develop' into author-class
Use esc_html__ in settings strings, add missing textdomain
Merge pull request #448 from x-team/author-class

Refactor author usage into WP_Stream_Author class; use System user always