lib/query: refactor & rework

- Move the lib/query/ stuff up a level into lib/
- Associate directly with the Query object
- Rework the Query object to be C++ rather than mixed with C
- Update all dependencies, tests

lib/test-mu-store.cc

@@ -26,7 +26,7 @@
 
 #include <locale.h>
 
-#include "test-mu-common.h"
+#include "test-mu-common.hh"
 #include "mu-store.hh"
 
 static std::string MuTestMaildir = Mu::canonicalize_filename(MU_TESTMAILDIR, "/");