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/main.cpp b/src/main.cpp
index ffa9f8d..08cd849 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -39,7 +39,7 @@
 
     for (auto& watch : ConfigPropertyWatches::get())
     {
-        watch->callback();
+        watch->callback(Context::START);
     }
 
     Loop::run();