Add statistic service to 'demo' assembly

[fboucquez]

Atm, the demo preset is using old versions of Faucet and Explorer. In order to upgrade, the demo preset must include the statistic service and a mongo db. The last time I tried, the statistic service returned empty lists when connected to a single node network (when a singleton node list was expected).

Once statistic service is upgraded, Explorer and Faucet can be too. Ideally, Faucet and Explorer should be able to connect to both status service node lists and a static node list for reliability (too fallback in case the static service is down).

[fboucquez]

Both demo and services assemblies would need update once the statistic service is refactored (and if it's possible to run in a container context, not just Lamba).

It would be great if both faucet and explorer can fall back to a static list of nodes for symbol test networks that don't have or require stats service.