Expose bitcoind RPC API to the host machine

[LaurentMT]

It seems that some users are willing to use the bitcoind packaged in docker as a source for external apps running on the docker host (e.g;: LN node, etc).

May be we could expose the port of the RPC API to the localhost, with something like

bitcoind:
  ports:
    - "127.0.0.1:28256:28256"

[kenshin-samourai]

a couple of remarks

• localhost isn't going to work when containers run in a vm (mac os, windows)
• make it optional? (default = no port exposed)

[kenshin-samourai]

Implemented in PR #8 as an option

Setup in /my-dojo/conf/docker-bitcoind.conf

• BITCOIND_RPC_EXTERNAL allows to expose/hide the rpc api outside of docker (default = hidden)
• BITCOIND_RPC_EXTERNAL_IP allows to set the correct ip address (default = 127.0.0.1)

Exposes the rpc api and zmq notifications (blockhash and rawtx)

Doesn't require a new install or an upgrade, just a restart of dojo

[LaurentMT]

It might be a good idea to expose all ZMQ ports when this option is activated.
Some apps rely on notifications which aren't required by Dojo.
(e.g.: lnd requires zmqpubrawblock source: https://gist.github.com/05nelsonm/ef55dcc1fb3aa588c8135cd107ee5d8c)

[kenshin-samourai]

support of additional ports and number of rpc threads implemented in PR #12