Refactor Background

[BalzaniEdoardo]

Currently, we have a background session. This should be replaced groups topics hierarchically. For example:

• Encoding Models: GLMs etc.
• Feature Construction: Basis, Convolution...
• Model Selection & interaction with scikit-learn

This sub-categories should contain some minimal math background and simple example code that showcase the functionality. For things like convolution over samples, we should highlight the NeMoS/pynapple interaction when multiple discontinuous epochs are represented in a pynapple object.

Examples in background should use simple simulated data.