Refactor out translation.h

This is a prerequisite for introducing bilingual error messages.
Note: #includes are arranged by clang-format-diff.py script.

src/index/txindex.cpp

@@ -6,6 +6,7 @@
 #include <shutdown.h>
 #include <ui_interface.h>
 #include <util/system.h>
+#include <util/translation.h>
 #include <validation.h>
 
 #include <boost/thread.hpp>