Several minor improvements to the website and documentation

[DavGoeck]

I was checking whether we can switch our current project's tests to Nightwatch and read through the documentation.

I found a few minor issues and thought I share them with you. If you prefer a separate ticket for each of these please let me know I will open them.

1. Links (Next / Previous) do not coincide with the order in Table of Contents (TOC) on the left.
   When I click on the "Next page" link and it takes me to a page different from what I would expect from the TOC. I understand this can be a choice and is not necessarily wrong, but the next page of "Selectors" is "Selectors", which I am sure is wrong.

2. If multiple sections are expanded in the TOC, then the lower part is cut off and cannot be scrolled to.

3. Some HTML-entities (") appear in the digest on the right of page: Define test environments.

4. Something is wrong with the whitespace in the Examples of page: Nightwatch on GitLab CI.

5. The ES6 arrows are wrong ( "=<" instead of "=>" ) in the Example on page: Debug Component Tests.

6. One of the mentions of "preRender" should be "postRender" on page: Write JSX react tests.

I am writing a PR for the last two issues: PR-276

[beatfactor]

Het @DavGoeck! Thanks for bringing this issues to our attention and glad to hear you're considering Nightwatch. Feel free to drop by our discord if you have any questions.

[nothuman2718]

@garg3133 I want to work on this.
Can you say is this architecture or bug?

The first point in the issue above

1. Links (Next / Previous) do not coincide with the order in Table of Contents (TOC) on the left.
   When I click on the "Next page" link and it takes me to a page different from what I would expect from the TOC. I understand this can be a choice and is not necessarily wrong, but the next page of "Selectors" is "Selectors", which I am sure is wrong.

[nothuman2718]

@garg3133 The point 2 in the above issue is working fine.
Can you check once?

[nothuman2718]

@garg3133 There is a simple fix for the above third point by removing double codes in headings. There may be a better fix, but I can come up with only this idea. If not, Please help.
This is the last one in the issue. With this change, the above issue can be closed.