services, backend and slowcontrol stuff

[marc1uk]

• fix order of teardown in Services class because SlowControlCollection could call ServicesBackend functions (alert callbacks), so we need to stop them SCC before SBE.
• In Services::Ready, wait for not just ServicesBackend::Ready but also SlowControlCollection::Ready. The former waits for all sockets to be ready, the latter just uses a monitoring socket to wait for the PUB socket, but this is probably sufficient.
• In Services::BufferThread, don't invoke SendMulticast if there's nothing to send.
• get verbosity from m_variables in Services::Init
• Fix missing mutex lock in ServicesBackend for pub monitoring socket check
• Put couts behind a verbosity check, so that it should not print anything (even errors) with verbosity 0. This is not ideal as we can't configure it to print errors only, but we need it to output absolutely nothing to stdout for use in a cgi, otherwise apache chokes.... :/
• move closing multicast sockets later in Finalise, and check in SendMulticast if they're open - if not, error
• add Ready check function to SlowControlCollection, uses socket monitor to wait for PUB socket (used for AlertSend) to be connected before returning - allows checking that AlertSend will do something.