Type of request

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Refactoring
• Documentation or documentation changes

Related Issue(s)

Closes #37

Concept

Description of the change

• Add GemException fatal state
• Add GemExceptionManager to the workbench context to be used for creatable classes and retrieve on the UI plug-in (also include the messages on the properties for i18n)
• Implement an abstract handler using the exception manager to inform user if the handler fails (and close the application if it is fatal)
• Use the new APIs where required

Checklist:

• All the commits are signed.
• My code follows the code style of this project.
• I agree with die CLA.
• I have read the CONTRIBUTING docs.
• I have added/updated necessary documentation (if appropriate).