[fr] follow 93c0542

Remove flash stuff from session docs, use Flash classes in examples
[fr] Follow #1430

3.0 - Add FlashComponent and FlashHelper docs
[fr] follow d72e897

Fix syntax error.
[fr] follow 112c864

Update migration guide for FlashComponent/FlashHelper.
[fr] follow #1434

Added information about new plugin structure and clarifying how to use
t..