Optimize calculating bonuses from buffs display

Only consider buffs that the player actually has. This considerably
improves the load time of the character pane. It goes from ~300ms to
~150ms for me.
Only calculate bonuses once

- For estimate functions, don't break down bonuses into categories.
  All callers just added them up anyway.
- Correctly add initiative bonus for The Vole moon sign

This buys ~50ms on charpane load time for me.