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/symbol/editor.cpp

@@ -16,6 +16,6 @@ void SymbolEditorBase::SetStatusText(const String& text) {
   control.parent->SetStatusText(text);
 }
 
-void SymbolEditorBase::addAction(Action* action, bool allow_merge) {
-  getSymbol()->actions.addAction(action, allow_merge);
+void SymbolEditorBase::addAction(unique_ptr<Action> action, bool allow_merge) {
+  getSymbol()->actions.addAction(move(action), allow_merge);
 }