Add a management command that combines committee summary totals and saves them to a new model

[aboutaaron]

A lot of the frontend work currently sits on loading totals and averages. These are all mgmt commands that need to be stored at the db layer.

We need to adjust our models to add this properties and then rope them in the database command with either an overwritten save() or with a management command.

[palewire]

This could be standard summary fields like total contributions summed by year, cycle and overall.