Fix karma loop exploit - Calculate individual stamp eigenkarma as if the user had given out no stamps

[plexish]

Right now there are some mild problems with the eigenkarma implementation (they were worse before Rob modified the proportion of stamps given out to stamps received from 1:1), which are due to the fact that who a user gives stamps to affects their own stamp score.

Have discussed this with Rob, and looks like we want a new function which we can call to find a non-exploitable stamp score for the user, and use this rather than the global one.

May make sense to store this and update it for a user when they receive a stamp? Would be a tiny bit inaccurate, but running it for each user on each stamp event may get expensive.

[tayler6000]

Consolidated into #136