fixed crashes on shutdown

1. In libp2p/Host: m_socked and m_acceptor should not outlive m_ioService, as it is required for proper destruction. Causes a segfault on windows.
http://www.boost.org/doc/libs/1_56_0/doc/html/boost_asio/reference/basic_io_object/_basic_io_object.html
http://stackoverflow.com/questions/18553886/clear-boostasioio-service-after-stop

2. In alethzero/MainWin: Changed destruction order to match the reverse construction order. WebThreeStubServer destructor requires connector to be alive.