We need a high level benchmark for testing the vochain performance, as pointed by issue #963.

This benchmark should be as realistic as possible (without requiring a network) and execute the whole stack: app, state, indexer and api.

A good starting point is this test: https://github.com/vocdoni/vocdoni-node/blob/master/test/api_test.go#L25

We might transform this test into a benchmark where the number of votes and parallel voting routines can be specified.

The benchmark should return the tempos required for performing an election of the specified size (from the creation to the result's scrutiny).

Note that the benchmarks on benchmarks/ directory are outdated, since all of them use the old RPC interface. However they can be used as example for the new benchmark.