Remove explicit code for destructors, and some constructors,
that are automatically defined by modern C++.
Also unpointerize a few objects.

Redmine: #2051
According to the reviewer recommendation from pull-request 533

Redmine: #2051

1. Underlying DataItem can be accessed only through dataItem method
2. If OutputData is not set, dataItem() throws an exception
3. Automatic choice of DataItem type depending on the rank of OutputData

Redmine: #2051

AutosaveService is adopted for new UpdateTimer. First working version of project autosave. Unit tests.