[enh] Add document/stats on UP peer (per API)
[enh] Add document/stats on members and pending membership

[enh] Compute stats on pending memberships

[fix] Network: filter on minBlockNumber only on the default peer filter

[enh] Use String for endpoint API, instead of enumeration (to allow to add api - e.g. GCHANGE_API)
[enh] Add /network/peering/peers (GET) action, using Duniter merkle tree
[enh] Add a cache on UP peers, used by /network/peers and /network/peering/peers, to avoid to many computation

[fix] Fix script 'cesium-plus-pod --help'