Adding freespacemode to OnbFreeSpaceProvider

Since our IT-Department told us to fill volumes uo to a certain percentage (95%), we indroduced the OnbFreeSpaceProvider, to make this work.
With new volumes we are now again allowed to fill it to 100%. But even with 100% more than 1,5 GB stays unused. We need to extend the OnbFreeSpaceProvider to a byte-mode, so that we can use all bytes which are available.