Airdrop campaigns can be clawbacked multiple times

[PaulRBerg]

Problem

MK-5 finding from BuildersDAO audit report:

Potential Solutions

1. Rename to latestClawback
2. Remove fields altogether
3. Remove clawback and introduce clawbacks array

Which one do you want to go with, @razgraf, @gavriliumircea? Not sure what the UI does at the moment.

And can you please create an issue?

[razgraf]

Renaming to lastClawback... sounds good.

[PaulRBerg]

#164