Decide on consistent naming for Base/Abstract classes

[mscroggs]

Currently, the base class for finite element is called FiniteElementBase while the base class for cells is called AbstractCell.

We should decide on a consistent naming for base classes. I'm in favour of the ObjectNameBase but am open to better opinions.

[wence-]

FooBase to me tends to suggest a concrete class that provides implementation for which one must call __init__, whereas AbstractFoo suggests an interface that a subclass must conform to (and therefore one doesn't need to call __init__). In #168 you're making an interface, so I think AbstractCell is right.

FiniteElementBase at the moment is in a superposition between these two states. It is kind of an interface, but requires that its subclasses set up the superclass appropriately (which some subclasses don't do and have to hack around). This has caused a bunch of pain in the past which I'm sure you are aware of! I think (although it's been a while since I looked concretely here) that the FiniteElementBase object should be an interface with no implementation and therefore by my internal guidelines would be named AbstractFiniteElement.

[mscroggs]

FiniteElementBase at the moment is in a superposition between these two states. It is kind of an interface, but requires that its subclasses set up the superclass appropriately (which some subclasses don't do and have to hack around). This has caused a bunch of pain in the past which I'm sure you are aware of! I think (although it's been a while since I looked concretely here) that the FiniteElementBase object should be an interface with no implementation and therefore by my internal guidelines would be named AbstractFiniteElement.

I'm working towards removing the __init__ from FiniteElementBase and making it more like an interface. I think it makes sense to then rename it AbstractFiniteElement.