Raw content return for Grid DataColumn & Column

Need to have a method  `getDataCellContent` to return raw parsed data cell content. This is useful when extending these Columns, for processing any other data before formatting via `renderDataCellContent`.
Raw content return for Grid DataColumn & Column

Need to have a method  `getDataCellContent` to return raw parsed data cell content. This is useful when extending these Columns, for processing any other data before formatting via `renderDataCellContent`.
Raw content return for Grid DataColumn & Column
Raw content return for Grid DataColumn & Column
Removed unnecessary blank space
Removed unnecessary blank space
first draft of the extension generator
added tests for smarty and worked around a small bug

fixes #2265
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.