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/monitor/fan.cpp b/monitor/fan.cpp
index 639d88e..17f5812 100644
--- a/monitor/fan.cpp
+++ b/monitor/fan.cpp
@@ -38,7 +38,7 @@
 
 
 Fan::Fan(sdbusplus::bus::bus& bus,
-         std::shared_ptr<sd_event>&  events,
+         phosphor::fan::event::EventPtr&  events,
          const FanDefinition& def) :
     _bus(bus),
     _name(std::get<fanNameField>(def)),