Allow some exceptions from extensions to pass through to the gui

[Nicklas Nordborg]

Exceptions that are thrown from extensions are normally only logged and then discarded. There is almost no way for the user to get informed about an error. Ticket #1545 would need such a feature for the "save" extension point. Eg. by throwing a certain error a "save" extension should be able to abort the save and have an error message displayed for the user.

[Nicklas Nordborg]

(In [5486]) References #1549: Allow some exceptions from extensions to pass thorugh to the gui

This is now implemented in the core extension system. An extension point may specify what ErrorHandlerFactory to use. We provide two implementations. One that only write to the log file (LoggingErrorHandlerFactory) and one that also re-throw the error so that it can bubble up to the gui (RethrowErrorHandlerFactory).

For extension points defined in XML files the error handler factory can be specified using the <error-handler-factory> tag. It uses the same sub-structure as other <*-factory> tags and has the same support for initialization.

[Nicklas Nordborg]

(In [5487]) Fixes #1549: Allow some exceptions from extensions to pass through to the gui

Documented in docbook. Show the configured error handler in the gui. Set a default error handler for the registry.

[Nicklas Nordborg]

(In [5488]) References #1549: Allow some exceptions from extensions to pass through to the gui

Let the error handler decide if the error should be stored in the registry or not. Typically we don't want to store the error, the exception so far is for service extensions.

[Nicklas Nordborg]

(In [5489]) References #1549: Allow some exceptions from extensions to pass through to the gui

Removing files that was accidentally added by [5488]. They belong to #1545

[Nicklas Nordborg]

(In [5520]) References #1549: Allow some exceptions from extensions to pass through to the gui

Updated some more documentation related to this.