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

extract util classes in own files

add another repository form for file system storage as jsons

add new type safe queries that translate to nspredicates and swift closures

add distinct filter to repository

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

bumb version number to 0.5.0

add convenience method

update tests and improve sort mode usability

remove closures and move all sort and filter functions to params of one function

clean up realm repository test cases