ExecServerThread & ServerThread rename

Now ExecRpcServerThread & RpcServerThread, respectively. Makes it clearer
to see the function name in the log on Linux builds (they don't show with
a namespace/class name by default).

Signed-off-by: James Warren <admin@trezanik.org>
Typedef thread types for ease of use

Win32: thread_t = uint32_t (thread ID)
POSIX: thread_t = pthread_t (typedef itself from unsigned long)

Signed-off-by: James Warren <admin@trezanik.org>