Simplified enable/disable of ilks

[brianmcmichael]

Simplifies the process of adding/updating/removing ilks. Removes the file function.

Addition of an ilk required four external file calls, this replaces additions and updates with an enableIlk(bytes32 ilk, uint256 line, uint256 gap, uint256 ttl) function.

• To add an ilk, call enableIlk("ETH-A", 500 * MILLION * RAD, 10 * MILLION * RAD, 1 hours)
• To update an ilk, call enableIlk("ETH-A", 800 * MILLION * RAD, 10 * MILLION * RAD, 1 hours) (requiring explicitness here will increase auditability in executives)
• To remove or disable an ilk, call disableIlk("ETH-A")

Open to alternative name ideas for functions/events

[gbalabasquer]

We could make on a boolean now, right?

[brianmcmichael]

Actually, we might not even need on anymore, now that I think about it. If we require in setup that line > 0, we can do require(ilks[ilk]).line > 0);, if so, it's enabled, since removing it deletes it from the mapping.

[gbalabasquer]

If we follow this approach maybe we can avoid using on at all and just check that ilkLine > 0.

[gbalabasquer]

lol I hadn't read your comment yeah let's go that way

[gbalabasquer]

But do you want to use require or the if return we have now?

[brianmcmichael]

Updated to remove on and enforce line > 0

[brianmcmichael]

fixed nits