Add classes for nav primary menu items and footer items

[richard015ar]

Issue: https://github.com/pressbooks/pressbooks-book/issues/781

Related PR: https://github.com/pressbooks/pressbooks-book/pull/821

This change adds 2 new classes for each top menu items: and for footer menu items: with the objective to allow users to customize the style. Classes added: For top menu:

nav--primary-item (for top menu items customization)
nav--primary-item-home (home item)
nav--primary-item-contact (contact item)
nav--primary-item-my-books (My Books item)
nav--primary-item-sign-out (Sign Out item)
nav--primary-item-sign-in (Sign In Item)

For footer menu:

footer__pressbooks__links__list-item (for footer menu items)
footer__pressbooks__links__list-item-guide-tutorials (Guide and Tutorials item)
footer__pressbooks__links__list-item-contact (Contact item)

Test notes

• Make sure you have this changes + changes in https://github.com/pressbooks/pressbooks-book/pull/821
• Log in as Admin and go to Appearance > Customize > Additional CSS
• Add different styles for the classes mentioned above and confirm users can add personalized styles to items.

[codecov-commenter]

Codecov Report

Merging #273 (9be5338) into dev (3f7cbb9) will not change coverage. The diff coverage is 0.00%.

:exclamation: Current head 9be5338 differs from pull request most recent head 43a0690. Consider uploading reports for the commit 43a0690 to get more accurate results

@@          Coverage Diff          @@
##             dev    #273   +/-   ##
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  Coverage   0.00%   0.00%           
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  Files          8       8           
  Lines        767     796   +29     
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- Misses       767     796   +29     

Impacted Files	Coverage Δ
inc/helpers/namespace.php	0.00% <0.00%> (ø)

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