Handle exception during Kitodo Script execution

[solth]

Fixes #5976

Also makes the "error-messages" list scrollable since it might contain many errors for many processes selected in the process list:

(edit: may therefor have some relevance for #3392 as well)

[BartChris]

The intended functionality is achieved: Adding data to a non-existing structural elements does no longer throw a Nullpointer exception. If multiple messages are displayed, the message is scrollable.
Code looks good. One might discuss wether it is necessary to catch the KitodoScriptExecutionException in case of calling deleteData, because as far as i can see, the exception will never be thrown in that case since no type is specified there. But maybe it is good to have the exception in place if this is changed in the future. (e.g. throwing an exception if a non existing metadata should be deleted)