Bug fix for assert_template when opening a new session.

See https://github.com/rails/rails/pull/16234#commitcomment-7115670.
Improve description of tests.
Add support for Postgresql JSONB

[Philippe Creux, Chris Teague]
adding indexes on tables in migration scripts

missed one migration script in last commit

remove some empty lines

using the belongs_to index option to be more concise
Add password:digest information to scaffold generator help text [ci skip]
Additional clarification on password:digest in scaffold and model generator help [ci skip]
Merge pull request #16272 from tgxworld/fix_template_assertion_when_opening_a_session

Fix template assertion when opening a session.
Merge pull request #16220 from pcreux/postgresql-jsonb-support

Add support for Postgresql JSONB
Merge pull request #16258 from mattwarrenrnp/master

adding indexes on tables in migration scripts [ci skip]
docs, add ref where to find valid `head` status symbols.

[ci skip]
Fix documentation of SQlite3Adapter.columns

As of https://github.com/rails/rails/commit/e781aa31fc52a7c696115302ef4d4e02bfd1533b SQLite3Column has been dropped.
Remove references to SQLite3Column from documentation
Merge pull request #16285 from noinkling/password_digest_docs

Add password:digest information to scaffold generator help text
Merge pull request #16290 from a3gis/master

[ci skip] Fix documentation of SQLite3Adapter.columns where SQLite3Column was removed in e781aa31fc52a7c696115302ef4d4e02bfd1533b
Fix that render layout should also be picked up by the template dependency tracker, but only half-ways. You can add that layout option on the same render call, and both templates should be added to the dependency tree. But thats going to require a more serious rework of the tracker. Please do help fix this part of it too. For now, render layout needs to be on its own line.