This PR replaces the clunky order-based mechanism to ensure metamodel files are loaded before parsing model files. This is done by introducing a language-specific option, which allows specifying one or more paths to .ecore files. As a consequence, the emf-model language no longer requires a submission order. As this is the only language that uses this feature, we can remove it. The corresponding methods in the Language interface are marked as deprecated.

While the prototypical DynamicEmfLanguage was never available in the CLI, it was available via the API. With this PR it is removed and only a deprecation placeholder remains. The EmfModelLanguage now depends on EMFLanguage instead of the DynamicEmfLanguage. All functionality that is still required is moved to the EmfModelLanguage.

Partly solves #576.

Work in progress, tasks left to do:

• Add more unit tests, especially regarding the metamodel path option.
• Adapt the readme to show how to specify metamodel files.
• Test if the language-specific option works with the jar.
• Decide if the EMF dynamic maven module and Language interface should be removed now or in a later release.

For release notes:

• EMF model language: Uses now the --metamodel CLI option to specify metamodel path(s) when loading the metamodel for EMF-based models.
• Breaking change: Deprecate the submission order functionality of JPlag languages.
• Deprecate the experimental dynamic EMF language, which was never available in the CLI.