Streamline web 3rd party dependencies

[calvellido]

• Complete jQuery removal for new default light theme.
• Improve anchors hover area by using absolute positions
• Use ES2015 syntax and newer APIs to improve code readibility
• Sidebar show/hide behaviour improvements
• Update highlightjs to version 9.16.2
• Update highlightjs license
• Get rid of unused files which were being copied unnecessarily
• Replace Bootstrap Font Awesome CDN URL to use Cloudflare standard one
• Make highlighting to happen once the DOM content has been loaded
• Change jQuery val name to avoid confusion now that jQuery is gone
• Update auxiliary languages highlighting through highlightjs to 9.15.10
• Make createResources method to copy only necessary hljs styles, not all
• Adjust docs header anchors to be shown in a more friendly way
• Make main page GitHub links to be external ones
• Make docs page GitHub links to be external ones
• Make rest of the external links really external by opening in new tabs
• Use https everywhere when valid
• Fix insecure deprecated http request on maven
• Fix all docs links, and start using them through the link tag
• Fix bad link with two slashes in the docs
• Small layout fxes for a vertically responsive behaviour on empty content
• Basic background slight improvements
• Browser console notice message 🤓
• Homogenize page layouts with the rest of them, make them all vertically responsive
• Slight style adjustments, having navbar in all layouts looking the same
• Add more semantic tags, and include a11y attributes
• Improve ScalaTags layout composing by using just TypedTags Lists

This closes #356

[AntonioMateoGomez]

Good job @calvellido !