Adds network contract system

[NataKilar]

Description of changes

Adds network contracts to the game, a method of managing group membership and regular/hourly payments to and from network accounts. Because contracts can themselves permit other users to grant certain contracts, this allows players to create business hierarchies analogous to those we've had in past iterations. In the future, a system for shares and majority control of contracts may be implemented.

This system is still a work in progress, and requires further testing and documentation