Fix generated twig paths for plugins : make them relative
Merge pull request #899 from romainneutron/plugins-absolute-dirs

[3.8] Fix generated twig paths for plugins : make them relative
Merge branch '3.8'

Conflicts:
	tests/Alchemy/Tests/Phrasea/Plugin/Management/AutoloaderGeneratorTest.php
Migrate demand table to doctrine entity && refactor registration API