Remove mock_model and stub_model from rspec-rails

Some tests still fail without them as I have not yet figured out
a good way to fix them yet. View scaffold generators are also
currently broken.

rspec/rspec-rails#894
Update generators and tests to use doubles/actual models
Update changelog
Update extracted game name in changelog to rspec-activemodel-mocks
Small cleanups for #902
This change will be released with rc1
Merge branch 'thomas-holmes-remove-mocks'