Canvas Item Decorator Support For Default error handler

[Michaelpalacce]

Description

We need to add support for a "Default error handler"

The default error handler is what is called in case of any uncaught errors in the workflow. It is a great way to have a last case error handling effort.

The "Default error handler" does not have anything pointing to it, but it has a target

Example

This is how the :Default error handler" looks like:

  <error-handler name="item5">
    <position y="200.0" x="140.0"/>
  </error-handler>

Notes

• The lack of anything targeting the "Default error handler" should be checked and enforced
• We should add support for target of course, this can point to any other element or end which will point to the end of the workflow
• The name in the error-handler is actually the "target", aka what will be called if an error is caught

[akantchev]

Implementation: #346