Fix serialization issues for rescheduling tasks.

[sergey-tsarevich]

Fix exception when it trying to save task with schedule then Exception is throwing:
com.fasterxml.jackson.databind.exc.InvalidDefinitionException: Java 8 date/time type java.time.ZoneRegion not supported by default: add Module "com.fasterxml.jackson.datatype:jackson-datatype-jsr310" to enable handling (through reference chain: com.github.bekk.exampleapp.model.TaskScheduleAndNoData["schedule"]->com.github.kagkarlsson.scheduler.task.schedule.CronSchedule["zoneId"])] with root cause.
Please see DynamicRecurringSchedulingTest.java

[geirsagberg]

Hey, I ran into a similar issue when having an Instant field in a task data. But I don't understand why the task data is serialized and deserialized, so I am making a simpler PR that simply removes the serialization

[geirsagberg]

I brought your tests into #117 , seems to work, so closing this one.