update proposition groups in specs as lists instead of sets, to preserve ordering for order-dependent correspondence functions
don't pass boundary region or obstacle names to nltkparser
temporary workaround to make 'stay there' work
updated dynamic letters spec
Merge branch 'nltkParser' of https://github.com/LTLMoP/LTLMoP into openworld
Merge branch 'spec_rewriting' of https://github.com/LTLMoP/LTLMoP into openworld