New tutorials on indexing and parameter sharing

[michaeldeistler]

This PR adds two advanced tutorials (setting synaptic parameter values and synaptic parameter sharing). As part of this, it modifies the outline of the website and splits tutorials into Tutorials and Advanced tutorials.

To make synaptic parameter sharing possible, this PR also contributes the .copy_node_property_to_edges() and adds tests for it:

net.copy_node_property_to_edges("global_cell_index")

df = net.edges
df = df.query("pre_global_cell_index in [3, 4]")
net.select(edges=df.index).set("Ionotropic_gS", 0.2)

[jnsbck]

I absolutely love this! Especially the use of pandas query, which I did not foresee being such a clean and powerful combination together with select.

I left a few comments. Good to go once addressed.