Implement feature that allows denormalization of vote counts

[lilsweetcaligula]

#43

Tests fail because the version of mem-store which supports upserts has not been released yet. When run against the latest mem-store via npm link, all tests pass:

$ npm run test

> seneca-vote@1.0.1 test
> ./node_modules/jasmine/bin/jasmine.js --config=test/support/jasmine.json

Randomized with seed 72004
Started
...................................................


51 specs, 0 failures
Finished in 1.979 seconds
Randomized with seed 72004 (jasmine --random=true --seed=72004)

[lilsweetcaligula]

For example, currently if the plugin crashes when trying to de-normalize a poll rating, the submission of the vote will not be rolled back (i.e. undone). This violates ACID and must be handled via implementation of a transaction.

[lilsweetcaligula]

Should we, perhaps, implement validation of the plugin options, passed to the plugin by the client? Such validation would be implemented in index.js, and make sure client passes supported well-formed options.