[DOC] Update and improve notebooks for classification

[TonyBagnall]

Describe the issue linked to the documentation

Update the classification notebooks along the following lines

1. merge and fix univariate and multivariate

#1536

2. Make the data formatting clearer with use cases for 2D, 3D numpy and dataframes

3. Use rocket and HC2 in examples

4. Include comparison to other algorithms and drawing a CD diagram

other suggestions welcome

[OliverMatthews]

With #1536 hopefully fixed now, I'll take a look at point 2 (making the data formatting clearer).

[MatthewMiddlehurst]

1, 2 and 3 are done. Unsure if 4 should be included, it should probably be a separate notebook if so. Thoughts @TonyBagnall?

[TonyBagnall]

Yes let's do it as another note book