Meassure a community's "membership power"

[olanod]

One of the metrics to promote a community to a higher rank in the Kreivo collective is their amount of memberships, but since memberships will come in different kinds and costs(e.g. a community can have members with "gold" memberships that cost much more than regular ones) then we can not just count the number of memberships a community holds to determine their rank increase.

I propose we track in the attributes of the community's collection a normalized sum that represents the total worth of the memberships that takes into account their duration and gas, that metric can be increased/decreased each time a community adds/removes a member. This scalar gives us an idea of how much "power"/commitment the community has with the protocol.

Note: how to account for expiring memberships?