[API break] Move all the tools in the tools directory instead of common.

The `common` name is from the time where kiwix was only one repository
for all the project (android, desktop, server...).

Now we have split the repositories and kiwix-lib is the "common" repo,
the "common" directory is somehow nonsense.

src/book.cpp

@@ -20,9 +20,9 @@
 #include "book.h"
 #include "reader.h"
 
-#include "common/base64.h"
-#include "common/regexTools.h"
-#include "common/networkTools.h"
+#include "tools/base64.h"
+#include "tools/regexTools.h"
+#include "tools/networkTools.h"
 
 #include <pugixml.hpp>