HeapSeparator: Implement preprocessings, rework heap separation accordingly

[alexandernutz]

In order for the heap separator to make use of the map equality domain, and separate the heap-array, we need to apply a preprocessing to the input program.

Problem:
To get a good separation result, we cannot simply analyze which values a pointer variable may have at any location in the program, but we want to know which values it could have at any heap-write that reaches the read-location.

We would like to try two flavours, both introduce a preprocessing before the map equality domain is applied:

1. "freeze-variables"
   at an array update l1: a[i] := v
   we add a nondeterministic update if (*) { frz_l1 := i }
   --> the analysis will derive all values that i can have during an update of a at location l1
2. "memloc-array"
   introduce a special global array called memloc
   at an array update l1: a[i] := v
   for every program location li, introduce a literal lit_li
   we add the statement memloc[i] := lit_l1
   --> the analysis will derive for every memory location i, at which locations it may have been written

The map equality domain will run on the preprocessed program, and afterwards the heap separator will transform the original program based on the analysis result.