Allow Delegators to Assign Beneficiary

[saulteafarmer]

I would like to see a feature added where a user could be delegating to postpromoter but elect to receive their payout at another user's address by sending a memo tx along the lines of:

assign @user (all/50sp/50000VEST)

The open bracket should be optional in my opinion. If a user doesn't specify then they would be assigning all of their rewards to be sent to USER but if they set 50 then the bot would only assign 50sp, etc.