Naming convention for NamedGraph graph generators

[JoeyT1994]

Going forward we should always adopt the naming convention that functions f which generate NamedGraph types are prefixed with named_f whilst the SimpleGraph version is simply f.

So for instance having named_hexagonal_lattice_graph versus hexagonal_lattice_graph and named_triangular_lattice_graph versus triangular_lattice_graph (two instances where we currently don't follow that convention).

We should also introduce:

named_random_regular, named_uniform_tree and others from [https://juliagraphs.org/Graphs.jl/dev/core_functions/simplegraphs_generators/] we wish to have easy constructors for.

[mtfishman]

Closed by #64.