permit auto-selling of stocks for users not present in server

[xiaowuc1]

The example that most easily motivates this - a user deletes their account. A deleted user should not be allowed to hold captive arbitrarily many securities.

If a user is not in the server, give admins the ability to auto-sell the securities that the user is holding to free them up for trading. Auto-selling gives the user the ability to reengage with trading if they rejoin the server and allows active members to trade on securities they otherwise wouldn't be able to trade on.

Alternatively, make this behavior happen by default when toggling when trading can be done.