Reorder Upgrade screen

[Detros]

In remembrance of this threads, here is a proper suggestion to reorder the Upgrade screen in other way than just chronological order of additions. Techs that are needed to use of some units should not be unlockable _after_ you unlock the unit. Or the unit infoscreen at least needs to note that needed tech. Also for newcomers, the Upgrade screen would make much more sense if similar units were together in one tree.

Could be problematic if people are only partly through the research, though, both code-wise (depends on the way unlocks are stored) and player-wise (they will temporarily lose access to steps they have access to and get access to other ones).