Add container aware trait
merged branch endroid/master (PR #8488)

This PR was squashed before being merged into the master branch (closes #8488).

Discussion
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Add container aware trait

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets |
| License       | MIT
| Doc PR        | will create one if merged

This trait can be used inside a class to make it container aware. As it is not always possible to extend the abstract ContainerAware class, the code for creating a container aware class is usually copied over and over (most of the time unchanged), resulting in a lot of redundant code in your project. As my projects are PHP 5.4 based nowadays, I would like to be able to use a trait in these scenarios to improve my workflow.

Commits
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4c9e606 Add container aware trait