This PR was merged into the master branch.

Discussion
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Change deprecated functions and remove unused imports

I changed the deprecated translation function setFallbackLocale() and the debug Exception- and Error-Handler.
Therefore i added symfony/debug to composer.json.

I also removed unused imports and fixed some classnames in docblock comments.

Commits
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d214e2e0 Test for TranslationServiceProvider
67c7e3fe Handle locale_fallback
380792b9 Also update doc for translation changes
60baeadc Remove unused imports and fix docblock for exceptions
69756f95 Use new debug component
92d4f0f1 Remove usage of deprecated function setFallbackLocale