Support for default ACL assignment

[hokster7]

When an object is 'saved' for the first time, its ACL should be set to Public Read/Write.
This is necessary to test that the beforeSave sets ACL's as appropriate.

[hokster7]

I found that it's not easy to include ACL when storing it into the mock collection. This is because when running a Parse.Query, the SDK falls over trying to build an ACL from an object that contains a '*' — I suspect you have to somehow map this public key descriptor object back to the API methods setPublicReadAccess() and setPublicWriteAccess().

Not sure what the solution is atm!