Voting: update forwarding radspec to factor in whether the forwarder has tokens or not

[sohkai]

In the majority of cases now, users do not have the direct ability to create new votes, so most votes are created via a forwarder (e.g. the Tokens app).

In these cases, the forwarders should not be holding voting tokens anyway (see #537), and we could change the radspec string for forward() to differ based on whether the msg.sender has tokens or not (see #1032 (comment) for confusion around the current text).