fix typo in string contains predicate

fix runtime crash when using empty predicate

add new compound and/or predicates

add string contains operator

add core data repository and tests

add another repository form for file system storage as jsons

Merge pull request #2 from quickbirdstudios/feat/remove-closures

Feat/remove closures

add perform transaction method

fix problem that objects were not deleted correctly

add support for nspredicates and fix typo