Replaces busy workers with running tasks on wq-status.
Fixes typo on -W, and shows tasks running rather than worker state.
Factorize out current_tasks_*command
Rewords help messages
Require explicit master for -T, -W
Merge pull request #223 from btovar/wq-status-show-number-of-tasks

1. Replaces busy workers with running tasks on wq-status. 
2. Some refactoring and cleanups. 
3. Require explicit master for -T, -W option in wq_status.