Add block and voters count in election information

[guilhermelawless]

Considered adding more details such as the number of votes for each block, but would need to tally up each election.

Similar to a previous PR, uses assert (!node.active.mutex.try_lock ()); which can have undefined behavior, but only used in Debug. Don't see an easy alternative in this case, and it was already used in election.cpp.

[cryptocode]

Most likely for a separate PR: I think you raise a good point about try_lock, even if it's in an assert. I know it's already done a couple of places, but election referencing node.active.mutex seems wrong to me. Not sure if we should add more of those. There are many data types that need external synchronization, and they generally don't reach out to an external mutex to see if it's locked. Maybe the cleanest solution is to put a mutex on election and make sure its properly encapsulated.

[guilhermelawless]

Agree 100%, see issue 2415 for tracking this. One glaring location is vote_processor::vote_blocking