Replace uses of `new` and `delete`

[DanRStevens]

The project has many occurrences of new and delete. These are best avoided in modern C++ code. Many of these (possibly all) can likely be replaced by std::unique_ptr. As a bonus, using std::unique_ptr may make some destructors empty, allowing us to omit them.

Reference: C.149: Use unique_ptr or shared_ptr to avoid forgetting to delete objects created using new

[ldicker83]

Generally in agreement here. There are cases where pointers make sense but I'm somewhat unfamiliar with so-called smart pointers. Seems now is as good a time as any to start moving the code in that direction.

[DanRStevens]

Did a quick scan of the code to see where we have naked new:

• Managing any class derived from State
• Managing map objects such as:
  • All Structure derived types
  • The Mine type
• The map TileMap
• Instances of ProductListBoxItem
• Classes used with Utility

Additionally, our choice of some external code forces some uses of new on us:

• TinyXML (particularly when creating XmlElement objects)
• Micropather

[ldicker83]

I do want to move away from TinyXML and reimplement with json. I've had a lot of success with https://github.com/nlohmann/json for json parsing, it feels very natural in C++.

Micropather we may want to consider adjusting to use without raw memory management. Might make sense to fork it for our purposes as the library really doesn't change much if at all or pull it out of the OPHD repository and add it as a submodule from its original source: https://github.com/leethomason/MicroPather

I think I added the code in before I really understood how to use git submodules :/