EFFECTIVENESS'. This commit changes the jam trace mechanism such that each 
entry in the jam trace buffer now will refer to a unique file id (JAM_FILE_ID) 
rather than a block number. This bringe the following benefits:
- It is much easier to map an entry to the right source code location.
  (Trace files will point to the source file rather than the block.)
- jam should be slightly faster, since the jam value can be calculated at
  compile time.
- Forgetting to call jamEntry() when going from one block to another is no 
  longer a problem. Each jam() call records the complete context. From
  now on, there is no need to add jamEntry() calls, jam() is sufficient.
- There is no need to maintain per-file jam offsets to distinguish between
  different files within a block.

See comments for jamFileNames in Emulator.cpp for a decription of how
to add new JAM_FILE_IDs.

This commit gathers include directives at the top of the source files
that have JAM_FILE_Ids. That way, it is easier to add a JAM_FILE_ID 
macro that will not be  redefined by some include file. Also, gathering 
include directives in one place improves code readability.

Notes:
* There were two cases of the following pattern: A.hpp defines class A. Then
  B.hpp in included, which defines class B and then defines inline methods for
  B which refers members of A. Finally A.hpp defines inline methods for A 
  which refers members of B. This mutual dependency means that A.hpp cannot 
  include B.hpp until *after* class A has been defined. It turned out that
  both cases of this pattern were due to methods that were not in use. 
  This was LogLevel::operator=(const EventSubscribeReq&) and 
  SignalCounter::operator=(const NodeReceiverGroup&). These methods have been
  removed such that the corresponding #include directives could be moved to
  the top.  

* SimulatedBlock.hpp had an unneeded #include of Mutex.hpp. This would not 
  compile unless Mutex.hpp was included after initial definitions in
  SimulatedBlock.hpp. Therefore, the #include was removed from 
  SimulatedBlock.hpp. Instead, Mutex.hpp is included directly from the files
  that need it.