Base class type alias convention.

I propose the following, which is compatible with our current coding conventions. Recall type should be the only entities with leading caps.

```C++
template
class Derived : public A
{
using Base = A;
void myMethod(auto A) { Base::member_var = A; }
...
}
```
Multiple inheritance (MI) case, only necessary if there is ambiguity
template
class Derived : public A, B
{
using BaseA = A;
using BaseB = B;
...
}
```