#12 Add support for long-lived objects

[Dimitrios Kolovos]

During the last workshop, Yannis mentioned that some of the objects he uses have a considerable start-up time and that it would be nice if he could use the same instances across different invokations of his metric providers. The obvious solution is to turn the respective classes to singletons but it may be something that we want to support at the platform level (e.g. platform.getLongLivedObject(Singleton.class))