add missing header end comments

- ensures a consistent usage in header files
- also add a blank line after the copyright header where missing
- also remove orphan new-lines at the end of some files

src/ui_interface.h

@@ -109,4 +109,4 @@ inline std::string _(const char* psz)
     return rv ? (*rv) : psz;
 }
 
-#endif
+#endif // BITCOIN_UI_INTERFACE_H