#227 Allow assigning input variables via SVG input mapping

It has been a while since we worked on this. What I want to do:

• Implement idea U1 from #203 (comment 273350) / #227
• Extend metamodel to a minimum
  • Update SvgIn element, make event optional and make updates with [0..*]. Parser should enforce one of the two is present.
  • Reuse Update element from Automaton.
• Extend parser to a minimum
  • Allow update to have general name, not just an identifier (was done in !190 (merged), that was never merged to develop, I will redo it).
  • Implement @SVGINKW IDKW Expression DOKW Updates OptSvgFile @SEMICOLTK
  • For now, don't implement @SVGINKW IDKW Expression EVENTKW SvgInEvent DOKW Updates OptSvgFile @SEMICOLTK

What still needs to be done:

• Everything related to simulator code.
• Everything related to HTML code generation.
• Tests for the typechecker and merge.
• Update Metamodel diagram images.
• Update LaTeX documentation.
• Update common methods (if applicable).
• Update CIF to CIF transformations and other tools.
  • The CIF merger would not be able to merge an svgin assignment with another specification that provides a non-input variable to be merged with the input variable, as then the svgin mapping would assign a non-input variable.
• Update CIF documentation.
• Update CIF example.

Addresses #227