upgrade "Upgrade" functionality

[sANDY]

after the introduction of mk4 sorters (also mk4 assemblers), there is a reason to increase the upgrade level to +3, because now only +2 levels can be upgraded, so there is no way I can upgrade mk1-> mk4 in 1 iteration, so I must have intermediate buildings in my inventory to do this

[Nekogod]

Although true, It seems quite unlikely you'd be upgrading from mk1 to mk4 directly though, at least not in any great quantity. I would imagine most of your factory would already be at mk2 or 3 by the time you're upgrading to mk4

[Sound]

The same happens from lvl 1 assemblers to re-composing assemblers, it's quite annoying.