Add callback contexts

Add the notion of a callback context. This enables callbacks
to have logic around the conditions they were invoked in.

There are two context on which call back can be invoked
1) Startup: during startup all the call backs will be called
2) Signal: As part of condition match on the watched properties.

Callback would behave differently based on the context.
eg: eventCallback
1) Startup: Don't take any action.
2) Signal: Create the Dbus Object for the event.

Change-Id: If455558798ac3e44bbd8a93de0ce1b09d2e308ae
Signed-off-by: Ratan Gupta <ratagupt@in.ibm.com>
diff --git a/src/journal.hpp b/src/journal.hpp
index cc74451..d9209af 100644
--- a/src/journal.hpp
+++ b/src/journal.hpp
@@ -31,7 +31,7 @@
             IndexedCallback(index), message(msg) {}
 
         /** @brief Callback interface implementation. */
-        void operator()() override;
+        void operator()(Context ctx) override;
 
     private:
         /** @brief Delegate type specific calls to subclasses. */