Replace direct Task.data access with a temp getter (syntactic refactor)

Now this getter, `data_removeme`, can easily be grepped out and
replaced, one usage at a time in small PRs.

src/rules.cpp

@@ -189,7 +189,7 @@ static void colorizeKeyword (Task& task, const std::string& rule, const Color& b
   // first match.
   else
   {
-    for (const auto& att : task.data)
+    for (const auto& att : task.data_removeme ())
     {
       if (! att.first.compare (0, 11, "annotation_", 11) &&
           find (att.second, rule.substr (14), sensitive) != std::string::npos)