Necromancer negative life tweaks

Makes a couple of tweaks to Necromancer's talents to prevent them from accumulating an excessively high ratio of positive/negative life:

If you know Blurred Mortality, half of the maximum life bonus from Constitution is instead added to your maximum negative life (in addition to its current effect). Your total effective life bonus does not change, but this does prevent Constitution from giving you more positive life than negative at high levels.

If you are a lich, half of the life you gain from levelling up will instead be added to your maximum negative life (counting the +life rating lichform already grants). The implementation might need some revision; additionally Lich already feels faceroll-strong so a buff of this magnitude might be overkill, although I believe it will ultimately feel better.