Fixes #2360: Added `AttributeBehavior` and `BlameableBehavior`, and renamed `AutoTimestamp` to `TimestampBehavior`
Merge branch 'master' of github.com:yiisoft/yii2

* 'master' of github.com:yiisoft/yii2:
  Fixes #2360: Added `AttributeBehavior` and `BlameableBehavior`, and renamed `AutoTimestamp` to `TimestampBehavior`
WIP merge ActiveRelation into ActiveQuery

allow extending only one class to add scopes, fixes #2146

TODO:

- [ ] adjust guide docs
- [ ] adjust README files of extensions
- [ ] finish work and fix test breaks
made createQuery() config param optional
Add ability to downgrade migrations by the absolute apply time
Add changelog line related to #2499
updated timestamp behavior in advanced app to renaming
fixed phpdoc errors and updated properties
updated classmap
added missing use statement
Some minimal doc blocks changes for consitency
Merge pull request #2500 from lucianobaraglia/master

Some minimal doc blocks changes for consitency
doc update about behavior.
Merge pull request #2499 from resurtm/migrate-to-datetime

Add an ability to downgrade migrations by the absolute apply time
Fixes #2487
Fixes #2460: custom listview/gridview summary was broken
Fixes #2458: Added missing validaton to advanced app forms, separated validation from email sending errors for contact form
Fixes #1578
merged ActiveQueryInterface and ActiveRelatioInterface
Fixes #2426: Changed URL creation method signatures to be consistent