Also convert the values for prime_tower_min_volume to make it behave similar to what the minimum volume used to be. This feature fixed a bug with the computation from volume to thickness. Now it's correct but we have to correct the old values to be still the same (approximately) as what used to be the end result.
Contributes to issue CURA-5457.
It may not be what the users often want to change, but it is something that they may be expecting to see in the custom settings mode by default. It's something that you often think of as a typical setting but in reality you don't often want to change it. Let's get closer to what the user expects. Requested by the support team of Ultimaker.
