- withdrawable -> unlocked
"withdrawable" was a bad name, since these funds - while unlocked -
are not necessarily withdrawable if the voter is currently engaged in
a vote.
- only_deposit -> only_unlocked
Locked funds are technically also deposited. Make it clearer that this
is talking about the unlocked parts of the funds on the account.
The vote power computation was broken for lockups that start very far
in the future.
- Fix the underflow itself
- Disallow lockups that start more than 100 years in the future
- Error if the lockup-scaled voting power is bigger than the maximum
lockup voting power