Clean up pointer use:

* Use unique_ptr for Actions instead of manual memory management
 * Use unique_ptr in KeywordDatabase
 * Use unique_ptr instead of shared_ptr for file formats
 * Don't pass shared_ptr to Reader/Writer, use references instead
Also
 * Switch to C++17 so we can use map::try_emplace

src/gui/value/editor.cpp

@@ -12,9 +12,9 @@
 
 // ----------------------------------------------------------------------------- : ValueEditor
 
-void ValueEditor::addAction(ValueAction* a) {
+void ValueEditor::addAction(unique_ptr<ValueAction> a) {
   if (a) {
     a->isOnCard(editor().getCard().get());
-    editor().addAction(a);
+    editor().addAction(move(a));
   }
 }

src/gui/value/editor.hpp

@@ -130,7 +130,7 @@ class ValueEditor {
   virtual DataEditor& editor() const = 0;
   
   /// Perform an action
-  void addAction(ValueAction* a);
+  void addAction(unique_ptr<ValueAction> a);
 };
 
 // ----------------------------------------------------------------------------- : Utility

src/gui/value/image.cpp

@@ -65,7 +65,7 @@ bool ImageValueEditor::canPaste() const {
 
 bool ImageValueEditor::doCopy() {
   // load image
-  InputStreamP image_file = getLocalPackage().openIn(value().filename);
+  auto image_file = getLocalPackage().openIn(value().filename);
   Image image;
   if (!image_load_file(image, *image_file)) return false;
   // set data

src/gui/value/text.cpp

@@ -856,7 +856,7 @@ void TextValueEditor::doFormat(int type) {
       break;
     }
     case ID_FORMAT_REMINDER: {
-      addAction(new TextToggleReminderAction(valueP(), selection_start_i));
+      addAction(make_unique<TextToggleReminderAction>(valueP(), selection_start_i));
       break;
     }
   }
@@ -983,7 +983,7 @@ void TextValueEditor::replaceSelection(const String& replacement, const String&
   fixSelection();
   // execute the action before adding it to the stack,
   // because we want to run scripts before action listeners see the action
-  TextValueAction* action = typing_action(valueP(), selection_start_i, selection_end_i, select_on_undo ? selection_start : selection_end, selection_end, replacement, name);
+  auto action = typing_action(valueP(), selection_start_i, selection_end_i, select_on_undo ? selection_start : selection_end, selection_end, replacement, name);
   if (!action) {
     // nothing changes, but move the selection anyway
     moveSelection(TYPE_CURSOR, selection_end);
@@ -994,7 +994,7 @@ void TextValueEditor::replaceSelection(const String& replacement, const String&
   size_t expected_cursor = min(selection_start, selection_end) + untag_for_cursor(replacement).size();
   // perform the action
   // NOTE: this calls our onAction, invalidating the text viewer and moving the selection around the new text
-  addAction(action);
+  addAction(std::move(action));
   // move cursor
   {
     String real_value = untag_for_cursor(value().value());