Add time Manager to handle property changes callback

1. Implement time::Manager who registers property change signal for time
mode and owner;
2. Add PropertyChangeListner interface to handle the callback;
3. Make EpochBase to implement the interface.

Change-Id: I185580ae37353e1ed82a47e4905fb22e269ac09d
Signed-off-by: Lei YU <mine260309@gmail.com>
diff --git a/Makefile.am b/Makefile.am
index 0af260f..066dd33 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -7,7 +7,8 @@
 libtimemanager_la_SOURCES = \
 	epoch_base.cpp \
 	bmc_epoch.cpp \
-	host_epoch.cpp
+	host_epoch.cpp \
+	manager.cpp
 
 phosphor_timemanager_SOURCES = \
 	main.cpp