Add endpoint / field to inform about the locked wallet

[cstenglein]

On startup when auto-unlock is not enabled, the Lightning wallet is locked.

I would like to have an extra endpoint or a field in ln_info_lite to see if the wallet is locked.

[fusion44]

I don't really want to add a field to ln_info_lite because you only can get this info when the wallet is unlocked.

Proposal:

All endpoints, while locked, will return http status 409 Conflict with a detail message that the wallet is locked. Additionally, when establishing the SSE connection, clients will receive a new event type called wallet_status with one boolean field locked. This way there is no additional endpoint needed, just to see whether the wallet is locked or not.

[cstenglein]

The SSE event sounds awesome!

I'm not sure if the 409 conflict though. How about 423 Locked :)

& a question: What endpoints won't work when the wallet is locked? Am I able to receive on-chain transactions etc.?

[fusion44]

See #34 for progress on this.