Reduce the use of `std::shared_ptr<>` where possible

[maxwellpirtle]

We use the C++11 std::shared_ptr<T> templated type to achieve some level of automatic reference counting. While storing references to transitions and objects benefits from the use of shared pointer, we should eliminate passing shared pointers, where possible, as arguments to functions and methods and instead pass the raw value directly. This will make the function declarations smaller and reduce any unnecessary reference counting inside each of the function calls. Furthermore, dereferencing the shared pointers requires one or two extra steps of indirection which would be avoided with raw pointers

[maxwellpirtle]

I used Valgrind's Callgrind tool and used KCachegrind to view some performance metrics for the MCMINI target (i.e. the target that is not transparent). I couldn't get callgrind to work correctly with the transparent McMini target but I'll keep fiddling with it. With debug symbols, it's pretty clear that the methods of std::shared_ptr<T> are heavily used.

Switching std::shared_ptr<T> to a reference type where possible will be our next performance priority

[gc00]

@maxwellpirtle , This sounds good. I would suggest using Valgrind/Callgrind in the non-transparent mode, making direct calls to McMini. The times will be almost the same. I doubt that Valgrind is smart enough to understand wrapper functions and dlsym.

[maxwellpirtle]

We should reinvestigate this a bit more. std::shared_ptr<> has its uses, some of which are probably still valid in the code base. However, it is used quite extensively and its use could perhaps be reduced or replaced with std::unique_ptr<> in some cases