Move headers from server/include to include/maxscale

- Headers now to be included as <maxscale/xyz.h>
- First step, no cleanup of headers has been made. Only moving
  from one place to another + necessary modifications.

server/modules/routing/testroute/testroute.c

@@ -12,8 +12,8 @@
  */
 #include <stdio.h>
 #include <maxscale/alloc.h>
-#include <router.h>
-#include <modinfo.h>
+#include <maxscale/router.h>
+#include <maxscale/modinfo.h>
 
 static char *version_str = "V1.0.0";