Cleanup old code (HTTP, Cluster)

[dnsmichi]

• SocketEngine*
• TlsStream
• JsonRpc::{Send,Read}Message
• HttpRequest/Response, HttpClientConnection, ApiClient
• Some features are also using the NetworkStream class which requires the TcpSocket class, this should be rewritten too.

Maybe it also is possible to rewrite the unix socket parts too.

[dnsmichi]

LivestatusListener uses Unix/TcpSockets with object inheritance on the Socket class, I'd like to get rid of this as well.

ExternalCommandListener uses a plain socket for the pipe, not sure if it is worth the hassle since this will be removed in 2.12 anyways.

[dnsmichi]

StreamReadContext with Netstring is something I'd like to get rid of as well, but likely in a separate attempt.

michi@mbpmif ~/dev/icinga/icinga2 (feature/network-cleanup>) $ grep -r StreamReadContext lib/
lib//compat/externalcommandlistener.cpp:		StreamReadContext src;
lib//cli/variableutility.cpp:	StreamReadContext src;
lib//cli/variableutility.cpp:	StreamReadContext src;
lib//cli/objectlistcommand.cpp:	StreamReadContext src;
lib//cli/troubleshootcommand.cpp:	StreamReadContext src;
lib//livestatus/livestatuslistener.cpp:	StreamReadContext context;
lib//base/configobject.cpp:	StreamReadContext src;
lib//base/stream.hpp:struct StreamReadContext
lib//base/stream.hpp:	~StreamReadContext()
lib//base/stream.hpp:	StreamReadStatus ReadLine(String *line, StreamReadContext& context, bool may_wait = false);
lib//base/netstring.cpp:StreamReadStatus NetString::ReadStringFromStream(const Stream::Ptr& stream, String *str, StreamReadContext& context,
lib//base/stream.cpp:StreamReadStatus Stream::ReadLine(String *line, StreamReadContext& context, bool may_wait)
lib//base/stream.cpp:bool StreamReadContext::FillFromStream(const Stream::Ptr& stream, bool may_wait)
lib//base/stream.cpp:void StreamReadContext::DropData(size_t count)
lib//base/netstring.hpp:	static StreamReadStatus ReadStringFromStream(const Stream::Ptr& stream, String *message, StreamReadContext& context,
lib//remote/apilistener.cpp:			StreamReadContext src;
lib//remote/httpchunkedencoding.hpp:	StreamReadContext& StreamContext;
lib//remote/httpchunkedencoding.hpp:	ChunkReadContext(StreamReadContext& scontext)
lib//remote/httpchunkedencoding.cpp:	StreamReadContext& scontext = context.StreamContext;

[dnsmichi]

Livestatus is a mess to rewrite, I'm leaving this for now in a WIP branch.