This PR was merged into the master branch.

Discussion
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Converters

This PR reverts #769 (which tried to fix #768) as this is a breaks BC for the most usual use case of converters (#806).

The decision has been taken (#814) that a converter always run, independently of the available request attribute names or controller argument names.

Because of the above, running the converters as a controller event is not needed anymore, and moving the converters earlier in the process gives more power to the developer (#825 and #826).

Commits
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a0644877 Convert request attributes in the KernelEvents::REQUEST event instead of KernelEvents::CONTROLLER event (closes #825)
3b207399 added a note about global  converters being applied to all controllers
76776926 Revert "merged branch igorw/convert-only-existing-attribute (PR #769)"