- handle existing morphed relations by avoiding eager loading in cert…

…ain scenarios

- ensure callbacks applied to items inside paginator

- avoid conflict with relation names and globally defined callables

- fixed https://github.com/OnlyExcel/laravel-base/issues/57

- allow applying callbacks to loaded relations

Handle nullable morphTo relations.

Added support for polymorphic relations.

Added toPaginator method.

Retain preserveKeys

Fixed array_shift by reference warning.

Fixed issue when loading belongsTo or hasOne relations inside a lengt…

…h-aware paginator.