Implement account_update_votes_operation

[xeroc]

This PR introduces a new operation account_update_votes_operation that we feel is necessary in conjunction with BSIP40 and allows for setting a separate key for updating account votes. It has been manged in BSIP40

[xeroc]

paging @Dimfred

[pmconrad]

Who is "we"? IMO it is premature to determine what may be necessary when BSIP-40 has not even been implemented.

AFAICS BSIP-40 does not mention specific additional operations. This would require a separate BSIP.

[xeroc]

Understood. Let us write a separate BSIP then.
The "we" is Blockchain Projects BV. We are currently growing our expertise in bitshares-core and would like to contriubute meaningfully .. This pull request as well as the #1368 come free of charge to the community.

[xeroc]

I finally figured out why you were asking 'who is we'. I of course did not intend to mix up different roles and simply forgot to distinguish myself as being somewhat part in core development and my role as CTO of BCP. Sorry about that.

As you can see from the author of the commit, the work here is provided by BCP and seeks feedback by the core team to figure out if this is the right way to go. A BSIP will be provided.

[xeroc]

Please find a pull request for a corresponding BSIP here

[sschiessl-bcp]

The separate voting mechanism makes sense to also reduce communication overhead when voting.

Voting should be a regular activity (and we will hopefully be able to battle voter apathy more efficiently in the future), but currently requires the whole account options to be serialized even if just one vote is changed. This increases the serialized transaction size significantly, and is also quite intransparent to the user because no one can be expected to check the whole account option object when changing one vote.

The mentioning of BSIP40 is not a direct dependency, but a use case. BSIP40 will allow to create a "voting key", and a separate voting operation will facilitate the creation of if significantly (without it complicated restriction on the account option object must be created).