EntryVisititor should use a unique_ptr<Store> instead of a raw pointer

[Ozaq]

EntryVisitor now uses an owned Store pointer. Coincidentally this pointer is released from a unique_ptr. However when just changing the code to use a unique_ptr I ran into circular dependencies between our headers, as I can no longer rely on a forward declaration when using a unique_ptr.

This is probably a bit of a pain to address but could help a lot with our code organization.

... this should be a unique_ptr as it is even initialized from the release of a unique_ptr in EntryVisitor.cc:46

Originally posted by @Ozaq in #54 (comment)