improve CASL amalgamability analysis

[sternk]

Reported by till and assigned to mcodescu Migrated from http://trac.informatik.uni-bremen.de:8080/hets/ticket/235

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In CASL.Amalgamability

• generalize for CASL extensions (at least for formulas. this is easy)
• optimisations in congruenceClosure (Nelson-Oppen algorithm?)
• optimisation in colimitIsThin (fixUpdRule)
• optimisations in the whole algorithm
• generate proof obligations

[sternk]

Comment by mcodescu Migrated from http://trac.informatik.uni-bremen.de:8080/hets/ticket/235#comment:2

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Amalgamability check does not terminate for the cocone computed with signature_colimit in case of Basic/Numbers.casl