require "active_support" is always needed

Per <https://github.com/rails/rails/pull/13605#issuecomment-31626172>,
always load the base "active_support" file before loading specific parts
of active_support.
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