Merge pull request #16027 from tgxworld/template_assertions

Fixes to ActionController::TemplateAssertions
Clear validators before and after each test

Or some tests fail when run in random order
remove deprecated `MissingHelperError` proxy.

The error was moved outside of the `ClassMethods` module.
ಠ_ಠ now that the commit sha is known I can add it to the relese guide.
Format
Make sure that fixtures are loaded before finding
[ci skip] updated 'where' in association documention to new style syntax
Merge pull request #8813 from greyblake/dont_write_timestamps_if_they_are_not_attributes

Write timestamps only if there are timestamps columns

Conflicts:
	activerecord/CHANGELOG.md
Ignore SCHEMA queries in some habtm tests
Fixed AR::Relation#where edge case with Hash and other Relation

Example:

  Author.where(posts: { author_id: Author.where(country_id: 1) }).joins(:posts)
Make ActionMailer::Previews methods class methods.
Refactor DeliverLater into MessageDelivery
Added ActiveJob configuration for travis
Merge pull request #16438 from agrobbin/input-placeholder-i18n

Add I18n support for `:placeholder` HTML option is passed to form fields
Merge pull request #16502 from bogdan/where-hash-nested-relation

[Regression 4.0 -> 4.1] Fixed AR::Relation#where edge case with Hash and other Relation
Warm up Symbols with where method

Looks like #first wasn't warm enough...
Merge pull request #16501 from tomkadwill/update_delete_to_new_style

[ci skip] updated 'where' in association documention to new style syntax
Use string for order argument, fixed from #16501 [ci skip]
Be sure to reset PK name renamed in the test
extract methods and metaprogram less.