Change the user message 'Logbook is empty'

This message is not appropriate because it is displayed:

• when the logbook is empty, no events are in the logbook at all
• when the filters are set such that no event is found.

In the second case, the message 'Logbook is empty' is wrong and will confuse people.

In order to distinguish between point 1 and point 2 (and display a different message for each), one could make an additional request to icat+ to get the count of all events in the logbook. This solution seems overkill to me at the moment.

The easiest solution is to change the message to:

'No log found'