Add IntvertibleBroadcastDiskArray

[rafaqz]

This idea is a generalisation of the CFDiskArray in DiskArrayTools.jl.

So a BroadcastDiskArray that also works for setindex! by having an inverse function that we call in writeblock!

We could even use InverseFunctions.jl to automatically detect the inverse function and allow inverted setindex even after a simple broadcast using dot syntax - without specifying the inverse function.