SBE course: further improvements

We added the first version of the SBE course in #742 (closed). This issue lists (potential) follow-ups.

• Review content
  • Detailed review by @ahofkamp.
  • Analysis of review comments made by @ahofkamp, performed by Asia.
  • Review by target audience.
  • Plan to address the comments by @ahofkamp and target audience.
• Improve content
  • Improve course based on reviews, according to the plan (see above).
  • Improve water lock case, as some things are modeled in a way that is maybe not recommended any longer.
• Extend content
  • Add an extra case (perhaps based on Module 6 from the students, or another case). See discussions at #742 (comment 2859537) and #742 (comment 2859923).
  • Revisit definition of 'language' once marking is introduced, as in Module 1.2 the language is defined as everything that can be reached.
  • Explain comments and @doc.
  • Explain in any for discrete variables.
  • Explain input variables.
  • Explain SVG input mappings with updates (to assign new values to input variables).
  • Explain supervisor vs controller, fault-tolerant control, controller checker, hardware mappings, code generation, etc.
  • Explain plant relations. (Or not, as in practice the relations don't always hold physically, unless the system can't break etc.)
• Improve style
  • Reconsider style of LaTeX state machines (state labels, events/keywords, variables, etc). Make sure each has a unique and distinguishable style, and make all images consistent with that.