Handle context/scope at the block level

[BPHarris]

The current FunctionAnalyser should be replaced with a BlockAnalyser with an added name attribute holding the function name for top-level functions, inner_func.outer_func for nested functions, etc. This BlockAnalyser should then be applied to all scoped contexts with the exception of classes (which remain a special case) i.e. functions, loops, nested functions.

This will allow for nested functions to be handled properly, but also for iterator names over an iterable in for loops to be treated the same way as arguments and parameters.