Clean up I18n stored translations after test.
Deprecate `serialized_attributes` without replacement

We've stopped using it internally, in favor of polymorphism. So should
you!
[ci skip] Update #has_secure_password docs
Merge pull request #15724 from akshay-vishnoi/secure_password_docs

[ci skip] Update #has_secure_password docs
docs, remove getting started guide sample application. [ci skip]

This application always gets out of sync and doesn't add much value.

Closes #15721

/cc @rafaelfranca
Merge pull request #15715 from zuhao/refactor_actionview_cleanup_I18n_translations

Clean up I18n stored translations after test.
Merge pull request #15704 from sgrif/sg-deprecate-serialized

Deprecate `serialized_attributes` without replacement
[ci-skip] correct wikipedia MVC link
Edit pass on `has_secure_password` documentation [ci skip]
Merge pull request #15734 from aditya-kapoor/correct-link

[ci-skip] correct wikipedia MVC link
[ci skip] update wiki link for MVC
Merge pull request #15735 from aditya-kapoor/update-wiki-md

[ci skip] update wiki link for MVC in README
reload I18n as we are defining `:ts` locale
fix build- see https://travis-ci.org/rails/rails/jobs/27578159#L2913.
Merge pull request #15737 from kuldeepaggarwal/fix-build

reload I18n as we are defining `:ts` locale  in  `test_number_to_human_with_custom_translation_scope`