A better support of different node types #597

We do have the node type parameter in the configuration, but it currently only affects what kind of p2p events a node is subscribed to.

The logic should be similar to the bitcoin one: https://github.com/bitcoin/bitcoin/blob/9e229a542ff2107be43eff2e4b992841367f0366/src/init.cpp#L419

Edit: it looks like at the moment the following is yet to be done here:

• Make sure that RPC transactions are still propagated in the "blocks-only-node" mode.
• Support "relay/forcerelay" permissions that would allow rebroadcasting transactions from certain peers.
  Note: "relay" allows to accept transactions from the peer even in -blocksonly mode; "forcerelay" specifies to always relay transactions from the peer, even if already in mempool.
  In bitcoin, the permissions can be specified as a part of -whitebind/-whitelist, and there are also the -whitelistforcerelay/-whitelistrelay options that set the corresponding permission for all whitelisted peers.