CIF language modification

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For each change to the CIF language, follow these steps:

Update textual syntax:
- Update cif.setext syntax (org.eclipse.escet.cif.parser/src/org/eclipse/escet/cif/parser).
- Update cif.bnf syntax (org.eclipse.escet.cif.documentation/images/language-reference/syntax).
- Update cif.min.js syntax (org.eclipse.escet.releng.configuration/highlightjs-assets/escet/languages/cif.min.js).
Update metamodel (org.eclipse.escet.cif.metamodel).
- Update Ecore diagrams (open model/cif.aird and unfold Design and then Entities in a Class Diagram).
- Update diagram images.
  - Remove all *.png files in the model/images folder of the CIF metamodel project.
  - Right click the cif.aird file in the Package Explorer` and choose Export representations as images.
  - Set To directory to the model/images folder of the CIF metamodel project.
  - Set Image Format to PNG.
  - Set Image Size to Nominal.
  - Click OK.
- Update genmodel.
  - Delete model/cif.genmodel.
  - Right click model/cif.ecore and select New Other….
  - Select Eclipse Modeling Framework and EMF Generator Model and click Next.
  - The parent folder and the file name should already be filled, click Next.
  - Select Ecore model and click Next.
  - Click Load and then Next.
  - For Root packages, select cif, for Referenced generator models, select Position, and click Finish.
  - Run model/autofix.py to update the newly created cif.genmodel.
- Generate metamodel code.
  - Remove the generated model code (contents of src-gen).
  - Open model/cif.genmodel.
  - Right click Cif and click Generate Model Code.
Update generated Java constructors and walker code (org.eclipse.escet.cif.metamodel.java).
- Remove the generated code (contents of src-gen).
- Right click gen-cif-constructors.launch and click Run As gen-cif-constructors.
- Right click gen-cif-walker.launch and click Run As gen-cif-walker.
Update LaTeX documentation (org.eclipse.escet.cif.metamodel).
- Right click gen-cif-docs-ecore-latex-skeleton.launch and click Run As gen-cif-docs-ecore-latex-skeleton.
- Right click gen-cif-docs-ecore-latex-skeleton-detail.launch and click Run As gen-cif-docs-ecore-latex-skeleton-detail.
- Update docs/cif_ecore_doc.tex based on the changes in docs/cif_ecore_doc_generated.tex.
- Update docs/cif_ecore_doc_details.tex based on the changes in docs/cif_ecore_doc_details_generated.tex.
- Run docs/build.bash to generate a new PDF.
Update parser (org.eclipse.escet.cif.parser).
- Right click gen-cif-scanner-parser.launch and click Run As gen-cif-scanner-parser.
- Implement new AST classes if needed.
- Update CifParserHooks.java such that it implements CifParser.Hooks.
- Verify the implementation by running chk.bash.
Update keywords and syntax highlighting for the text editor (org.eclipse.escet.cif.texteditor).
Update type checker (org.eclipse.escet.cif.typechecker).
- Add new constraints to the error and problem messages (ErrMsg.java).
- Verify the implementation by running chk.bash.
Update example and benchmark models for changed syntax and constraints (org.eclipse.escet.cif.examples).
Update pretty printer including set of keywords (org.eclipse.escet.cif.prettyprinter).
Update common methods (org.eclipse.escet.cif.common).
Update CIF to CIF transformations and other tools.
Update CIF documentation, including language reference manual with lexical syntax and grammar.
Update CIF syntax highlighting definition for LaTeX (org.eclipse.escet.cif.misc/latex/cif_listing.sty).