Adds LocalDistinguishability function

A month ago I had started to write a State Distinguishability Toolbox. Well, I decided to reduce all of it to just ONE file and ditch the toolbox :)

Still WIP :construction:

Some notes:
- I only check for bosonic extension, I will modify the code to take into account non-bosonic extensions too;
- I treat the case of distinguishability by PPT measurements as a special case where the number of symm. extension copies is equal to 1. In SymmetricExtension.m I see that positivity of partial transpose is checked on the subsystems `1:ceil(k/2)+1`. When `k=1`, this calculates the partial transpose on both the subsystems,
which is just the transpose. Is that "ceil" supposed to be "floor", or I can't use it for the case k=1?
(see https://github.com/nathanieljohnston/QETLAB/blob/master/SymmetricExtension.m#L106)
Is checking for partial transpose only on that cut the strongest thing we can do?

@nathanieljohnston @vprusso