Revert "merged branch igorw/convert-only-existing-attribute (PR #769)"

This reverts commit e7d4a2fdedee2f55d1581659865ebb764f5cadad, reversing
changes made to d6fe48eaf37e511eef606446012ebf50c68735d2.

Conflicts:
	doc/changelog.rst
	src/Silex/EventListener/ConverterListener.php
added a note about global  converters being applied to all controllers
Convert request attributes in the KernelEvents::REQUEST event instead of KernelEvents::CONTROLLER event (closes #825)
feature #828 Converters (fabpot)

This PR was merged into the master branch.

Discussion
----------

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
-------

a064487 Convert request attributes in the KernelEvents::REQUEST event instead of KernelEvents::CONTROLLER event (closes #825)
3b20739 added a note about global  converters being applied to all controllers
7677692 Revert "merged branch igorw/convert-only-existing-attribute (PR #769)"