Allow users to vote/unvote for a list of BPs on a given chain

[nsjames]

It needs to be clear to users that there is a 3 day time limit between unvoting and getting back tokens, and that undelegating BW causes a reduction in voting power

[kesar]

Delay its only for unstack, but votes are removed instantly, is it like that? worth to test in order to give a clear msg