Manage account and peer config on a running connector

[adrianhopebailie]

Similar to #446 it would be useful to be able to manage the accounts, plugins and connections configured without needing to restart the whole connector.

This should also be done via an admin API.

Suggested commands would be:

• connect/disconnect plugin
• adjust plugin options (e.g. server URL)
• add new account
• adjust account settings such as balance min and max plugin, asset, scale (TBD which are a good idea)
• force a settlement
• graceful shutdown of an account (stop accepting packets, settle account, disconnect)
• dump current config to file (to use if the connector is restarted)

[SolsticeLLC]

Would also like to see the clearing of payment channel for a given peer or moneyd client added into this enhancement. Of particular interest would be identifying any payment channels in an errored state - such as only being set up on one side and not on the other end. Would also be good to be able to see the payment channels in the Moneyd-gui and be able to perform the cleanup functions there.