Allow limit to null to get the entire list of resource.

Here is my use case :

I have about 20 to 30 products, and i want all of my product on a single
page without pager or limit.

My config is

_sylius:
    paginate: false
    limit: null
    sorting: { releasedAt: desc }

Without my change i got 0 product because of the int cast inside
getLimit method
Merge pull request #301 from BenoitLeveque/allow-no-limit-without-pager

Allow limit to null to get the entire list of resource.