Consolidate pointer-aliasing analyses

Original issue created by @PhilippWendler on 2017-09-07 at 15:35:46, last modified on 2017-09-07 at 18:24:02

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Currently there are at least two CPAs for pointer-alias analysis, the AndersenCPA and the PointerCPA (in the pointer2 package). It should be evaluated whether these two CPAs can be merged into a single CPA, which should be sound and fast enough such that it can be added to most standard configurations of CPAchecker.