Resolves #142 Garbage collect peer objects

Does not used shared ptrs due to complexity of threading situation. Instead peer objects are garbage collected only when all thread jobs are idle to ensure no other thread is possibly using the object.

components/net/cpp/include/ftl/net/universe.hpp

@@ -217,6 +217,7 @@ class Universe : public ftl::Configurable {
 	std::thread thread_;
 	std::list<ReconnectInfo> reconnects_;
 	size_t phase_;
+	std::list<ftl::net::Peer*> garbage_;
 
 	struct ConnHandler {
 		callback_t id;