Create `MultiModel` examples

[jajcayn]

The plan is to have three notebooks showcasing MultiModel.

Basic run + connected model (ALN + thalamus)

• done ?

• basic MultiModel run with neurolib wrapper, show star parameters and how they work
• more advanced heterogeneous model (2 nodes -> brain net), use example with thalamus + ALN

Creating a new MultiModel model

• done ?

• build a Jansen-Rit model
• show and build NeuralMasses for JR model
• build a single node for the model
• showcase full network - JR network with few nodes, and-or JR for cortex + thalamus

Advanced topics

• done ?

• showcase both backends and why there are two backends and which to which
• show exploration with MultiModel
• show evolution with MultiModel
• show how already implemented models can be easily adapted by subclassing NeuralMasses and/or Nodes