Reconstruct Kontrol's functionality related to minimization and merge node

[Stevengre]

Some codes related to minimize_proof and merging node are not correct, e.g.,

• Doesn't support merging node functionality

kontrol/src/kontrol/foundry.py

Line 910 in eb61949

KCFGMinimizer(proof.kcfg).minimize()

• Doesn't support merging node correctly (miss the hueristic for merging node)

kontrol/src/kontrol/foundry.py

Line 1119 in eb61949

apr_proof.minimize_kcfg(merge=options.merge)