Convert votes into entities

Currently the poll votes are stored in the poll_votes table however the data is not a field or an entity. I am working on this to get past the hurdle of not having to use another contrib module to fully supporting migration from previous drupal versions.

I am considering the value of changing it to an entity and also having the following fields:

1. id - a requirement for entities?
2. uuid - it seems all entities have these. I am unsure if it is strictly necessary?
3. value - a numerical field, default value of 1, that can be used to extend the module to allow the poll_vote entity to be used other type of polling. Currently this can be used (as a more expensive?) version of count but in the future it will allow extension to allow different vote values and even different votingsystems such as rating or ranking. Those will need more work on the Poll entity (follow up, not for this issue).