Optimize PeriodicTask.schedule, Hook.recipients and other fields
Optimize PeriodicTask.schedule, Hook.recipients and other fields

* Fix bug with MySQL and utf8mb4 encoding.
* Remove index creation on HistoryLines for better performance.
* Change max_length for Variables.key, Task.name.

polemarch/ce#172

vstconsulting/polemarch,vstconsulting/polemarch,vstconsulting/polemarch,vstconsulting/polemarch