Extension token locking

[kronosapiens]

Closes #921

Supports #915, allowing extensions (here, VotingToken) to lock & unlock user's tokens.

[area]

Unfortunately, while I think this implementation is now fine, I don't think it can be merged in the current state. The problem is that with the existence of the VotingReputation contract (which can call arbitrary functions on a colony with a root motion), anyone can unlock anyone else's tokens arbitrarily if this function is introduced.

[kronosapiens]

Ah! You're so right. I think the fix here is to add a mapping of [extension][lockId] => bool so you can only unlock the locks you've created.

[area]

Also unfortunately, such a mapping cannot be trusted because of recovery mode.

[kronosapiens]

@area I don't think that's a major concern. A lot of things "cannot be trusted" because of recovery mode, but by definition it's a highly trusted mode so I'm not worried. If anything we could call it a feature -- a bug was found in an extension, we need to remove the lock so we "give" the lock to another voting contract, etc. Using recovery mode as part of an attack on a token lock seems like much more trouble than it's worth.

[area]

You've not commented on my changes to the tokenlocking event or the requireExecuteCall changes so I assume you're good with them 😛

[kronosapiens]

Definitely :)