Make query classifier self-contained.

Only the query classifier needs the functionality of the embedded
server, while the rest of MaxScale is content with the client
library or Connector/C.

This have now been rearranged so that query-classifier links with
the embedded static library and then explicitly exports its own
functions using the query_classifier.map linker script. That way
query classifier will use the embedded library, while the rest of
maxscale use the client library, and this without conflicts.

Currently, query_classifier is not linked to maxscale-common,
but executables must link to maxscale-common and query_classifier.

server/core/poll.c

@@ -36,6 +36,7 @@
 #include <mysql.h>
 #include <resultset.h>
 #include <session.h>
+#include <query_classifier.h>
 
 #define         PROFILE_POLL    0