Display [unsaved] logs

[NeumannJoerg]

So far two developers asked, if it was possible to display an unsaved log.

The intention was to collect messages during runtime without saving them.
After processing the log should have been displayed to create a comprehensive output.

This is currently not possible, as /usi/cl_bal_lstate_active clears the message buffer after saving.
In order to display an unsaved or partly saved log, saved messages need to be reloaded from the database.
Additionally function module /usi/bal_popup_message_details relies on the data containers being saved to the database.

As this seems to be a valid use-case it should be made possible.