relay-server: handle channels gracefully

[daemon1024]

• use select for non-blocking channel operations instead of goroutines, noting this will skip sending the log if channel is blocked for some reason https://gobyexample.com/non-blocking-channel-operations
• bring back Map Structure Lock to prevent data races, we removed the lock because channel handing was blocking which caused issues but was not the right way to proceed.
• close channel after deleting client to prevent memory leaks

Ref #15

[nyrahul]

The primary fix seems to be that of closing the connection.
I see that the locks have returned. Is the point that now that we close the connection, the log sent to broadcast channel would fail (and not get stuck) since we are closing the connection?

[daemon1024]

@nyrahul the primary fix here is usage of select. Select chooses the non blocking cases, if our channel is blocking it will choose the default case and move on to next iteration.

Closing the channel is just a safety measure to prevent memory leaks since after deleting the client from our map structure, the channel pointer would dangle waiting to be garbage collected.

[nyrahul]

Tested the PR. This fixes #15