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/set/stats_panel.cpp

@@ -238,7 +238,7 @@ void StatDimensionList::drawItem(DC& dc, int x, int y, size_t item) {
   StatsDimension& dim = *dimensions.at(item - show_empty);
   // draw icon
   if (!dim.icon_filename.empty() && !dim.icon.Ok()) {
-    InputStreamP file = game->openIn(dim.icon_filename);
+    auto file = game->openIn(dim.icon_filename);
     Image img(*file);
     if (img.HasMask()) img.InitAlpha(); // we can't handle masks
     Image resampled(21, 21);