Split IOHook into IOHook and IOHookProvider

Create one IOHook instance for each hooked socket which contains all the
hook specific data and read/write/close functions, removing the need for
the "issl_session" array in SSL modules.

Register instances of the IOHookProvider class in the core and use them to
create specialized IOHook instances (OnConnect/OnAccept).

Remove the OnHookIO hook, add a dynamic reference to ListenSocket that
points to the hook provider (if any) to use for incoming connections on
that socket.

For outgoing connections modules still have to find the IOHookProvider
they want to use themselves but instead of calling AddIOHook(hookprov),
now they have to call IOHookProvider::OnConnect() after the connection
is established.