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
Changed markdown library to cebe/markdown

- supports GFM now
- allows defining different flavors

fixes #47
fixed several issues with apidoc generator
Merge pull request #2471 from yiisoft/markdown

Changed markdown library to cebe/markdown
env. config fixed
visibility fix
added test-case to frontend unit tests
Merge pull request #2478 from Ragazzo/yii2_advanced_tests_fixed

Yii2 advanced tests fixed
test typo fix
Merge pull request #2479 from Ragazzo/yii2_advanced_tests_typo

test typo fix
mongodb method "open" not triggered event "after open connection"
add method findOne() to the Collection class
small typos
refactoring Session component