convert all shoulds and stubs to expects, matching rspec 3 style

RSpec 3 now `expect`s (see what I did there) a departure from the `should` and `stub` syntax, causing depreciation warnings when running the test suite:

>Deprecation Warnings:
>
>Using `should_receive` from rspec-mocks' old `:should` syntax without explicitly enabling the syntax is deprecated. Use the new `:expect` syntax or explicitly enable `:should` instead. Called from /Users/trey/Developer/napa/spec/active_record_extensions/stats_spec.rb:28:in `block (2 levels) in <top (required)>'.
>
>Using `should` from rspec-expectations' old `:should` syntax without explicitly enabling the syntax is deprecated. Use the new `:expect` syntax or explicitly enable `:should` instead. Called from /Users/trey/Developer/napa/spec/authentication_spec.rb:8:in `block (3 levels) in <top (required)>'.

I've gone through and converted the files that were raising the depreciation errors.