This PR was squashed before being merged into the 2.0.x-dev branch (closes #1445).

Discussion
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Fix some deprecations from Twig and Symfony

Commits
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c5506448 changed a test to help debugging
72d7746e added support for Twig runtime loaders
147d7cc0 fixed Twig deprecation notices
d2dab720 added 3.2 in test matrix