Add capability to freeze token Accounts

[CriesofCarrots]

An authority may want the ability to "freeze" specific accounts.

Add a new authority to the Mint and a new initialized state variant to Account. The authority is able to toggle that variant for an associated account. Setting the variant to "frozen" disables any changes from being made to the account, ie transfer in or out, approve, revoke, set-authority, burn.

Fixes #229

[CriesofCarrots]

@mvines @jackcmay , wdyt?

Also:

• Currently, it is the same instruction to freeze and account as it is to unfreeze: ToggleFreeze. We could split into two, or ask the user to pass a parameter to indicate which action is intended, if we want extra assurance that the account is intended to be frozen (or unfrozen). Thoughts?
  Update: parameter added
• Currently, only the freeze_authority can sign to update the freeze_authority on the Mint. I considered giving this power to the Mint owner as well, but it seemed a little unnecessary to me. Does that sound okay?

[mvines]

• Currently, it is the same instruction to freeze and account as it is to unfreeze: ToggleFreeze. We could split into two, or ask the user to pass a parameter to indicate which action is intended, if we want extra assurance that the account is intended to be frozen (or unfrozen). Thoughts?

I far prefer passing a parameter.

• Currently, only the freeze_authority can sign to update the freeze_authority on the Mint. I considered giving this power to the Mint owner as well, but it seemed a little unnecessary to me. Does that sound okay?

Keeping the authorities completely separate seems ok to me. Freeze is arguably more powerful than Mint, but I like the idea of not having to order them

[jackcmay]

While you have eyes on the token program, open to any way to reduce the loads of copypasta in the tests

[CriesofCarrots]

@jackcmay @mvines , ready for another look!

While you have eyes on the token program, open to any way to reduce the loads of copypasta in the tests

I'll take a look! Separate pr.

[CriesofCarrots]

Bump @jackcmay @mvines

[CriesofCarrots]

@mvines @jackcmay got the COption clean up in and CI is happy. How is this looking?

[mvines]

looking really good overall

Pull request has been modified.