(Feature, Core) Some optimizations and "Load more ballots" button for "All" tab

[varasev]

(Mandatory) Description This PR makes Voting DApp display only first ten ballots and display "Load more ballots" button below the ballots list in "All" section:

It also adds optimization for reading validator metadata and efficiently usage of new smart contracts.

Relates to https://github.com/poanetwork/poa-dapps-voting/issues/118, https://github.com/poanetwork/poa-dapps-voting/issues/124, https://github.com/poanetwork/poa-dapps-voting/issues/128 and https://github.com/poanetwork/poa-dapps-voting/issues/132.

(Mandatory) What is it: (Fix), (Feature) or (Refactor) (Feature)

[varasev]

@vbaranov Ok, I fixed that in https://github.com/poanetwork/poa-dapps-voting/pull/139/commits/e5ce111130bde12271ad0e459723a65bdc52e270 and did some refactoring. Now the search works for all cards (even hidden by Load more ballots button) and the button takes into account only items satisfying the search criteria.

[varasev]

I've added a new commit https://github.com/poanetwork/poa-dapps-voting/pull/139/commits/287735aed83a59080d54a59b1d46dbc20ac9b77d collapsing core and demo branches.

[varasev]

Was updated DApp checked with poa-test-setup scripts?

@vbaranov Yes, it was. It can be checked with poa-test-setup from my repo: https://github.com/varasev/poa-test-setup - it is bound with all the latest changes (new smart contracts and updated Voting DApp and Validators DApp).