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/data/format/apprentice.cpp

@@ -301,7 +301,7 @@ void ApprDistroDatabase::removeSet(const String& code) {
   // TODO ?
 }
 
-void ApprDistroDatabase::doRead(InputStream& in) {
+void ApprDistroDatabase::doRead(wxInputStream& in) {
   wxTextInputStream tin(in);
   ApprDistro* last = 0;
   while (!in.Eof()) {