Update Tutorial with new major improvements.

[HansOlsson]

In particular MCPs - could see if we can link to them; see #3672

From @casella:

• Initial equations to compute initial states and fixed = false parameters. This is absolutely essential
• Balanced components: this concept was introduced in Modelica 3.x, I think it is a key concept to introduce when talking about information hiding. I think the tutorial should introduce a simplified version of it, e.g. not considering inner/outer, stream, etc., and refer to the specification for the full version
• Stream connectors: these are widely used for thermo-fluid systems, we should probably introduce them
• Overconstrained connectors: this is a more advanced concept, maybe it could be introduced in a simple case, such as propagation of phase/frequency information in 3-phase system models
• Operator records and their application to Complex numbers should also be mentioned
• clocked synchronous systems
• state machines. These are rather advanced topics, but they are self-contained, so we could also add them to the Tutorial.

I believe they can each contain references; so no need to update the general reference list.