This patch resolves several bugs:
* NetworkServer would allocate various instances of `NetworkClientInfo`.
This is patched by deallocating the NetworkClientInfo when it's
listening thread ends in the `listen_done` section.
* Memory would be allocated for threads that wouldn't be freed. This
is resolved by detaching from the threads, so they no longer need to
be joined to be freed, and then freeing the memory as they finish.
* Thread-Safety issues involving `ServerClients` would result in stray
`NetworkClientInfo`'s not being removed from the list in certain
situations. This is resolved by used a mutex to lock access to this
from different threads.
