Use unique_ptr for sd_event object wrapper

Convert the sd_event object wrapper from a shared_ptr to
a unique_ptr.  Requires a new header file.

Change-Id: I868a9e88ed93878c2e0bb12e58f8d3a604510da0
Signed-off-by: Matt Spinler <spinler@us.ibm.com>
diff --git a/timer.cpp b/timer.cpp
index 41a8138..d371c98 100644
--- a/timer.cpp
+++ b/timer.cpp
@@ -27,7 +27,7 @@
 
 using namespace phosphor::logging;
 
-Timer::Timer(EventPtr& events,
+Timer::Timer(phosphor::fan::event::EventPtr& events,
              std::function<void()> callbackFunc) :
     timeEvent(events),
     callback(callbackFunc),