Introduce HMBKP::refresh_schedules to force schedules to be reloaded from the DB and use it when re-setting up the default schedules.

Fixes #458
Let's die instead of just echo'ing the error message as it's cleaner
Don't strip 0 from minutes in the schedule sentence otherwise 10 becomes 1

Instead use intval to strip preceding 0's
s/dpesnt\'t/doesn\'t
Only show the total calculated schedule size when editing a schedule

Otherwise the new schedule form is really slow to open as it has to re-calculate the whole size of the site everytime.