improve public grafana dashboard

[altergui]

after MVP #83 some issues were left unresolved:

• when the nodes are starting, the spit out misleading stats. ideally, avoid reporting stats while the node is syncing (or starting up) (cf. public grafana dashboard #83 (comment))
• "elections by type" is not trivial as the other stats, since there's no code in place to calculate this. I'd need to implement this first in the indexer, adding such a query: indexer: query to count elections by type vocdoni-node#1114
• i'd love to also calculate the amount of total tokens (i.e. circulating supply) but is also not trivial, again i'd need to touch the indexer, and i don't even see any code related to tokens until now (only token txs). planned in indexer: track accounts, balances and extend API vocdoni-node#1050

i'd also add a few low hanging fruit i see in #23

Track usage metrics for the protocol:

• Nº Orgs
• Nº active processes
• Nº of processes with at least 1 vote