Adhoc Context for ContextCollectors

The use of wns::probe::bus::ContextCollector is too complicated. It is not always needed to use the ContextProviderCollection and ContextProvider to fill context of a measurement. The users needs to write too much code to simply get a local variable transported on the probe bus as context when a measurement is made. This blueprint proposes an extension to the ContextCollector API that simplifies the process. Furthermore, the user does not need to deal with the ContextProviderCollection if it is not needed. The base usage is then reduced to (pseudo-code)

  double MeasurementValue = 1.234;
  wns::probe::bus::ContextCollector cc_("probeBusName");

  cc_.put(MeasurementValue, "IntegerKey", 1, "StringKey", "hello", "MoreKeys", "world", "EvenMore", 1);

The argument list after MeasurementValue should have a dynamic length. And each key, value pair should be put the the measurements context. Also you do not need to provide a ContextProviderCollection to the constructor of a ContextCollector. If it is not provided an empty collection is constructed by default.