reusable navbar template

[dhmlau]

Before making changes to navbar, it's better to make it reusable so that we only need to change it in one file instead of multiple files. This PR contains:

• adding navbar-template.html - navbar template that is extracted from other pages
• modifying the *.html to use the template
• updating the jquery library. The "slim" version won't work, so use the "min" version instead.

To test locally, you need to start the server (run npm start), instead of viewing it as a file because it has jQuery scripts.

[nabdelgadir]

Tested it out locally, and it seems like it's no longer changing the colour for the page you're on.

See Getting Started is darker in the current one:

[nabdelgadir]

add new line here