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/commands/CmdDenotate.cpp

@@ -128,7 +128,7 @@ int CmdDenotate::execute (std::string&)
       }
     }
 
-    if (before.data != task.data)
+    if (before.data_removeme () != task.data_removeme ())
     {
       auto question = format ("Denotate task {1} '{2}'?",
                               task.identifier (true),

src/commands/CmdImport.cpp

@@ -198,7 +198,7 @@ void CmdImport::importSingleTask (json::object* obj)
     if (hasGeneratedEnd)
       task.set ("end", before.get ("end"));
 
-    if (before.data != task.data)
+    if (before.data_removeme() != task.data_removeme())
     {
       CmdModify modHelper;
       modHelper.checkConsistency (before, task);

src/commands/CmdModify.cpp

@@ -79,7 +79,7 @@ int CmdModify::execute (std::string&)
     Task before (task);
     task.modify (Task::modReplace);
 
-    if (before.data != task.data)
+    if (before.data_removeme () != task.data_removeme ())
     {
       // Abort if change introduces inconsistencies.
       checkConsistency(before, task);

src/commands/CmdUDAs.cpp

@@ -134,7 +134,7 @@ int CmdUDAs::execute (std::string& output)
   std::map <std::string, int> orphans;
   for (auto& i : filtered)
   {
-    for (auto& att : i.data)
+    for (auto& att : i.data_removeme ())
       if (! Task::isAnnotationAttr (att.first) &&
           ! Task::isTagAttr (att.first) &&
           ! Task::isDepAttr (att.first) &&