mainapp: Fix missing includes

Tested:
    Built and run through unit tests.

Change-Id: Iede17218b421f2694135600683c7ad185b8766f4
Signed-off-by: William A. Kennington III <wak@google.com>
diff --git a/mainapp.cpp b/mainapp.cpp
index 1aa69e5..b8c84c9 100644
--- a/mainapp.cpp
+++ b/mainapp.cpp
@@ -22,6 +22,10 @@
 #include <phosphor-logging/elog-errors.hpp>
 #include <phosphor-logging/elog.hpp>
 #include <phosphor-logging/log.hpp>
+#include <sdbusplus/bus.hpp>
+#include <sdbusplus/exception.hpp>
+#include <sdbusplus/server/manager.hpp>
+#include <sdeventplus/event.hpp>
 #include <string>
 #include <xyz/openbmc_project/Common/error.hpp>