cancancan added

refs #133 Authenticate pages #16 Add cancancan

I don't see much use for cancancan right now, but maybe in the future with recommendations

As for authenticating pages, here is what I thought of:
Users should not see purchase history of other users --> already taken care of
Users should not see cart view of other users --> cart#show takes care of this
Non-admins should not see dashboard --> taken care of in other PR

so basically this PR is to just setup cancancan for use in the future..