Implement create, alter and drop workload management triggers

Implement triggers for workload management:

The commands to be implemented:

CREATE TRIGGER `resourceplan_name`.`trigger_name` WHEN condition DO action;
condition is a boolean expression: variable operator value types with 'AND' and 'OR' support.
action is currently: KILL or MOVE TO pool;

ALTER TRIGGER `plan_name`.`trigger_name` WHEN condition DO action;

DROP TRIGGER `plan_name`.`trigger_name`;

Also add WM_TRIGGERS to information schema.