#593 Allow annotations on specifications

• Best to review per commit.
• Design decisions:
  • Allow annotations in the metamodel on all components. Currently only used for specifications. Will be extended later. This is similar as for declarations.
  • Annotations for specifications must be at the start of the file, before any other elements, for consistency with other elements, where the annotations must also precede them.
  • Annotations for specifications use double @ signs, to be able to distinguish between annotations for the specification itself and for the first element of the specification.
• Other changes:
  • CifAnnotationsTypeChecker doesn't need descriptionSupplier, and therefore now only has one public method (overload).
  • Generated Simulink code gets empty line between file header comment and imports, for consistency with generated C code.
  • Small comment improvement in ConvertFromEventBased.
  • Small textual fixes in lexical syntax page of the CIF reference manual.

Addresses #593