EventContext in k4FWCore and functional algorithms

[m-fila]

In Gaudi functional the algorithms' operator() can accept an EventContext that will be provided by the scheduler. In k4FWCore functional algorithms it's not allowed. Both Gaudi and k4FWCore non-functional algorithms accept EventContext in their execute

The EventContext holds information about:

• a concurrent slot used by the event,
• event number (ordinal number given by scheduler)
• id consisting of event id and run id (to be set from event data).
  In the k4FWCore the standard way of supplying event id and run id is with an EventHeaderCollection data object so this is not used currently

The EventContext information could be still useful for less-standard algorithms like EventHeaderCreator #224. The EventContext run id and event id is used in some logging statements but is never set in k4FWCore so a dummy (uninitialized?) value is used

This is not a big problem and rather invisible during "standard" usage. I create this item mostly to keep track of differences between standard Gaudi facilities and k4FWCore