Importing same task the second time crashes CH

When importing task definition xml for the first time CH works normally. However if the same task is imported for the second time, the CH instance that executes that task crashes.
This is related to the fact, that CH uses the task ID from the imported task. And because the task already exists, the new task tries to use the same database for storage which conflicts with the other task.

There are 2 problems here:
1. Re-using the task ID - CH should either reject such import with a message, or change the ID (possibly by asking user if that's what he want to do).
2. Unhandled exception related to serialization. It should be caught by default and a message should be displayed with the appropriate information.