Fix bugs and Improve visual experience

[ain-soph]

The first bug

https://pytorch.org/tutorials/beginner/audio_preprocessing_tutorial.html#mel-filter-bank

It should be a - rather than + in the right-menu.

The bug is introduced by the wrong class. There should be no not-expanded class.

<a class="reference internal not-expanded expanded" href="#mel-filter-bank">Mel Filter Bank</a>

The second bug

in jquery javascript of right-menu, we use$(href) to search for item in article with that id (e.g., href=#torch). However, it doesn't work if '.' in href (e.g., #torch.nn.Softmax), because jquery will regard nn and Softmax as classes. It requires backslashes '\\' to escape the dot.

This doesn't affect current pytorch docs, because there is no dot in right-menu items. But if we put the classes and methods generated by autodoc into the right-menu, which will leads to many problems. torch.nn.Softmax as an example.

The third bug

sphinx 4.2.0 modify <div class="section"> to <section>, which makes some of our css setting not work, which causes the margin-top for each section not 0 (It should be 0 according to css), further leading to the visual bug for the right-menu at page bottom (because the height offset is calculated with wrong numbers.).

https://pytorch.org/tutorials/beginner/audio_preprocessing_tutorial.html

Hide shortcut-wrapper at page bottom.

https://pytorch.org/tutorials/beginner/audio_preprocessing_tutorial.html
In Tutorial, shortcut-wrapper get overlapped at page bottom. So I think it's better to hide it.