Spyder: Improvements to the Help panel

[dalthviz]

Problem Description

• [x] Change Note sections colors on the dark them
• [x] Change default snippets colors on the dark theme (from Monokai to Spyder Dark)
• [x] Add loading page
• [x] Unify hover and click vs Ctrl + I results (for example with spyder/spyder/app/restart.py doing Ctrl+I when the cursor is just before a parenthesis)
• [x] Change table style

[ccordoba12]

@dalthviz, as part of this effort, please also change the style of "Note" sections (which is the same of "See also" ones, I think):

This is the docstring of plt.plot.

[ccordoba12]

@dalthviz, please also take a look at this other bug. If you press Ctrl+I next to this function:

https://github.com/spyder-ide/spyder/blob/62de40c4005c9ca30be5c83bdbd6f366a3fccd42/spyder/app/restart.py#L62-L71

you'll get as a result in the Help pane:

However, when you hover on the function and make a click on that hover, you'll get:

As you can see, the second result is the right one because it includes the header and the function signature, whereas the first one is missing those elements.

[ccordoba12]

@dalthviz, let's take this opportunity to also improve the style of tables in both the dark and light themes:

These are my suggestions:

• Add a line to bottom border of the table.
• Please align the the table headers (i.e. character and description in the screenshot above) to the left.
• Please reduce the top and bottom padding around text in each cell by two or three pixels (please post screenshots here to see how it looks with different paddings).

[dalthviz]

@ccordoba12 a preview of the tables with the changes suggested above:

[ccordoba12]

Things look much better now, thanks @dalthviz! But please reduce the top/bottom padding in each cell a bit more.