Schedrem

feat: exit schedrem --action command with its subprocess's exit status

fix: exit if another SchedremManager is running

fix: handle ValidationError on --action

feat: return exit status 1 if schedrem --action with yesno prompt is answered "No"
fix: validate_sound() should also accept WAV in uppercase
fix: remove unnecessary information from weekday not in weekdaynames error

feat: return exit status 1 if schedrem --action with yesno prompt is answered "No"

Add "enabled" option to schedule config.