[ui] Use human-readable format for data sizes
The ISO image size and the USB flash drive capacity are always displayed in MiB which is not optimal for large sizes as you can see in the following screenshot:
As you can see the USB flash drive capacity is displayed as 30000 MiB. It should be displayed in GiB which is more sensible.
Solution: Use QLocale::formattedDataSize
to display data sizes in a human-readable format