server: minor refactoring

Move files into a server subdirectory to correspond to the 'server'
namespace and create a 'server.hpp' as method to gain includes
needed by any server instance.  Create a few type aliases to
reduce namespace levels.

Change-Id: I8f8ea8e57177393faa007351a540d08873d36632
Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
diff --git a/tools/templates/interface.mako.server.cpp b/tools/templates/interface.mako.server.cpp
index 382ae7c..63bc788 100644
--- a/tools/templates/interface.mako.server.cpp
+++ b/tools/templates/interface.mako.server.cpp
@@ -1,5 +1,4 @@
-#include <sdbusplus/bus.hpp>
-#include <sdbusplus/message.hpp>
+#include <sdbusplus/server.hpp>
 #include <${"/".join(interface.name.split('.') + [ 'server.hpp' ])}>
     <%
         namespaces = interface.name.split('.')