Add set struct domains

[jakoberzar]

The existing struct abstract domain in Goblint (Simple) is a mapping from struct fields to their abstract values. It does not keep any information about relations between the fields.
We have tried to improve the struct domains in Goblint by adding two new domains (Sets and KeyedSets) that keep this information by using a set of mappings from fields to abstract values.
We have also added a third domain that can be picked within FlagConfiguredStructDomain that selects the struct domain dynamically depending on the struct field types.

I have squashed all of my commits into one.
Feel free to suggest improvements to the code. Currently, some code is kind of duplicated between Sets & KeyedSets (and some with HoareSet), I don't know how to solve that best.

[michael-schwarz]

I suggest we merge this and then do any further required changes by need.

[sim642]

I'm kind of bothered about the amount of copy-paste code from HoareDomain as well, because that adds two more Hoare domain implementations to the list in #101 (comment).

[michael-schwarz]

All x could indeed be redefined via let x = x_with_fct x but I'm not sure if that makes the code nicer to understand overall.

[michael-schwarz]

The copy-paste from the HoareDomain in some sense seems inevitable to me, unless we are willing to equip it with those x_with_fct functions (which are needed for structs that contain arrays), but feel like they are leaking abstraction.

Even if we are willing to do that, there will still be some code to handle the particular weirdness of these partitioned arrays, that we will not be able to abandon.

[sim642]

I guess the partial duplication of Hoare domain can stay, otherwise this will never get merged.

For the cases where I pointed out op being different from op_with_fct, maybe just add comments to acknowledge this mismatch.

[michael-schwarz]

I redefined all operations x in terms of x_with_fct now (where appropriate).